diff --git a/README.md b/README.md
index 3bd6a0d..72aa91d 100644
--- a/README.md
+++ b/README.md
@@ -179,14 +179,14 @@ whether the first character in the argument is a quotation mark.
 
 ```js
 { type: 'function', sourceIndex: 0, value: 'url', before: ' ', after: ' ', nodes: [
-     type: 'string', sourceIndex: 5, quote: '"', value: '/gfx/img/bg.jpg' },
+    { type: 'string', sourceIndex: 5, quote: '"', value: '/gfx/img/bg.jpg' },
 ] }
 ```
 
 ### unicode-range
 
-The unicode-range CSS descriptor sets the specific range of characters to be 
-used from a font defined by @font-face and made available 
+The unicode-range CSS descriptor sets the specific range of characters to be
+used from a font defined by @font-face and made available
 for use on the current page (`unicode-range: U+0025-00FF`).
 
 Node-specific properties:
@@ -195,7 +195,7 @@ Node-specific properties:
 
 ## API
 
-```
+```js
 var valueParser = require('postcss-value-parser');
 ```
 
@@ -258,6 +258,6 @@ Stringifies the node tree.
 
 Walks each node inside `parsed.nodes`. See the documentation for `valueParser.walk()` above.
 
-# License
+## License
 
 MIT © [Bogdan Chadkin](mailto:trysound@yandex.ru)
diff --git a/lib/index.d.ts b/lib/index.d.ts
new file mode 100644
index 0000000..8759f3f
--- /dev/null
+++ b/lib/index.d.ts
@@ -0,0 +1,177 @@
+declare namespace postcssValueParser {
+  interface BaseNode {
+    /**
+     * The offset, inclusive, inside the CSS value at which the node starts.
+     */
+    sourceIndex: number;
+
+    /**
+     * The offset, exclusive, inside the CSS value at which the node ends.
+     */
+    sourceEndIndex: number;
+
+    /**
+     * The node's characteristic value
+     */
+    value: string;
+  }
+
+  interface ClosableNode {
+    /**
+     * Whether the parsed CSS value ended before the node was properly closed
+     */
+    unclosed?: true;
+  }
+
+  interface AdjacentAwareNode {
+    /**
+     * The token at the start of the node
+     */
+    before: string;
+
+    /**
+     * The token at the end of the node
+     */
+    after: string;
+  }
+
+  interface CommentNode extends BaseNode, ClosableNode {
+    type: "comment";
+  }
+
+  interface DivNode extends BaseNode, AdjacentAwareNode {
+    type: "div";
+  }
+
+  interface FunctionNode extends BaseNode, ClosableNode, AdjacentAwareNode {
+    type: "function";
+
+    /**
+     * Nodes inside the function
+     */
+    nodes: Node[];
+  }
+
+  interface SpaceNode extends BaseNode {
+    type: "space";
+  }
+
+  interface StringNode extends BaseNode, ClosableNode {
+    type: "string";
+
+    /**
+     * The quote type delimiting the string
+     */
+    quote: '"' | "'";
+  }
+
+  interface UnicodeRangeNode extends BaseNode {
+    type: "unicode-range";
+  }
+
+  interface WordNode extends BaseNode {
+    type: "word";
+  }
+
+  /**
+   * Any node parsed from a CSS value
+   */
+  type Node =
+    | CommentNode
+    | DivNode
+    | FunctionNode
+    | SpaceNode
+    | StringNode
+    | UnicodeRangeNode
+    | WordNode;
+
+  interface CustomStringifierCallback {
+    /**
+     * @param node The node to stringify
+     * @returns The serialized CSS representation of the node
+     */
+    (nodes: Node): string | undefined;
+  }
+
+  interface WalkCallback {
+    /**
+     * @param node  The currently visited node
+     * @param index The index of the node in the series of parsed nodes
+     * @param nodes The series of parsed nodes
+     * @returns Returning `false` will prevent traversal of descendant nodes (only applies if `bubble` was set to `true` in the `walk()` call)
+     */
+    (node: Node, index: number, nodes: Node[]): void | boolean;
+  }
+
+  /**
+   * A CSS dimension, decomposed into its numeric and unit parts
+   */
+  interface Dimension {
+    number: string;
+    unit: string;
+  }
+
+  /**
+   * A wrapper around a parsed CSS value that allows for inspecting and walking nodes
+   */
+  interface ParsedValue {
+    /**
+     * The series of parsed nodes
+     */
+    nodes: Node[];
+
+    /**
+     * Walk all parsed nodes, applying a callback
+     *
+     * @param callback A visitor callback that will be executed for each node
+     * @param bubble   When set to `true`, walking will be done inside-out instead of outside-in
+     */
+    walk(callback: WalkCallback, bubble?: boolean): this;
+  }
+
+  interface ValueParser {
+    /**
+     * Decompose a CSS dimension into its numeric and unit part
+     *
+     * @param value The dimension to decompose
+     * @returns An object representing `number` and `unit` part of the dimension or `false` if the decomposing fails
+     */
+    unit(value: string): Dimension | false;
+
+    /**
+     * Serialize a series of nodes into a CSS value
+     *
+     * @param nodes  The nodes to stringify
+     * @param custom A custom stringifier callback
+     * @returns The generated CSS value
+     */
+    stringify(nodes: Node | Node[], custom?: CustomStringifierCallback): string;
+
+    /**
+     * Walk a series of nodes, applying a callback
+     *
+     * @param nodes    The nodes to walk
+     * @param callback A visitor callback that will be executed for each node
+     * @param bubble   When set to `true`, walking will be done inside-out instead of outside-in
+     */
+    walk(nodes: Node[], callback: WalkCallback, bubble?: boolean): void;
+
+    /**
+     * Parse a CSS value into a series of nodes to operate on
+     *
+     * @param value The value to parse
+     */
+    new (value: string): ParsedValue;
+
+    /**
+     * Parse a CSS value into a series of nodes to operate on
+     *
+     * @param value The value to parse
+     */
+    (value: string): ParsedValue;
+  }
+}
+
+declare const postcssValueParser: postcssValueParser.ValueParser;
+
+export = postcssValueParser;
diff --git a/lib/parse.js b/lib/parse.js
index d9d995f..950631c 100644
--- a/lib/parse.js
+++ b/lib/parse.js
@@ -50,16 +50,21 @@ module.exports = function(input) {
         after = token;
       } else if (prev && prev.type === "div") {
         prev.after = token;
+        prev.sourceEndIndex += token.length;
       } else if (
         code === comma ||
         code === colon ||
-        (code === slash && value.charCodeAt(next + 1) !== star)
+        (code === slash &&
+          value.charCodeAt(next + 1) !== star &&
+          (!parent ||
+            (parent && parent.type === "function" && parent.value !== "calc")))
       ) {
         before = token;
       } else {
         tokens.push({
           type: "space",
           sourceIndex: pos,
+          sourceEndIndex: next,
           value: token
         });
       }
@@ -91,22 +96,25 @@ module.exports = function(input) {
         }
       } while (escape);
       token.value = value.slice(pos + 1, next);
-
+      token.sourceEndIndex = token.unclosed ? next : next + 1;
       tokens.push(token);
       pos = next + 1;
       code = value.charCodeAt(pos);
 
       // Comments
     } else if (code === slash && value.charCodeAt(pos + 1) === star) {
+      next = value.indexOf("*/", pos);
+
       token = {
         type: "comment",
-        sourceIndex: pos
+        sourceIndex: pos,
+        sourceEndIndex: next + 2
       };
 
-      next = value.indexOf("*/", pos);
       if (next === -1) {
         token.unclosed = true;
         next = value.length;
+        token.sourceEndIndex = next;
       }
 
       token.value = value.slice(pos + 2, next);
@@ -126,6 +134,7 @@ module.exports = function(input) {
       tokens.push({
         type: "word",
         sourceIndex: pos - before.length,
+        sourceEndIndex: pos + token.length,
         value: token
       });
       pos += 1;
@@ -138,6 +147,7 @@ module.exports = function(input) {
       tokens.push({
         type: "div",
         sourceIndex: pos - before.length,
+        sourceEndIndex: pos + token.length,
         value: token,
         before: before,
         after: ""
@@ -193,6 +203,7 @@ module.exports = function(input) {
               {
                 type: "word",
                 sourceIndex: pos,
+                sourceEndIndex: whitespacePos + 1,
                 value: value.slice(pos, whitespacePos + 1)
               }
             ];
@@ -204,21 +215,25 @@ module.exports = function(input) {
             token.nodes.push({
               type: "space",
               sourceIndex: whitespacePos + 1,
+              sourceEndIndex: next,
               value: value.slice(whitespacePos + 1, next)
             });
           } else {
             token.after = value.slice(whitespacePos + 1, next);
+            token.sourceEndIndex = next;
           }
         } else {
           token.after = "";
           token.nodes = [];
         }
         pos = next + 1;
+        token.sourceEndIndex = token.unclosed ? next : pos;
         code = value.charCodeAt(pos);
         tokens.push(token);
       } else {
         balanced += 1;
         token.after = "";
+        token.sourceEndIndex = pos + 1;
         tokens.push(token);
         stack.push(token);
         tokens = token.nodes = [];
@@ -232,8 +247,10 @@ module.exports = function(input) {
       code = value.charCodeAt(pos);
 
       parent.after = after;
+      parent.sourceEndIndex += after.length;
       after = "";
       balanced -= 1;
+      stack[stack.length - 1].sourceEndIndex = pos;
       stack.pop();
       parent = stack[balanced];
       tokens = parent.nodes;
@@ -279,12 +296,14 @@ module.exports = function(input) {
         tokens.push({
           type: "unicode-range",
           sourceIndex: pos,
+          sourceEndIndex: next,
           value: token
         });
       } else {
         tokens.push({
           type: "word",
           sourceIndex: pos,
+          sourceEndIndex: next,
           value: token
         });
       }
@@ -295,6 +314,7 @@ module.exports = function(input) {
 
   for (pos = stack.length - 1; pos; pos -= 1) {
     stack[pos].unclosed = true;
+    stack[pos].sourceEndIndex = value.length;
   }
 
   return stack[0].nodes;
diff --git a/lib/stringify.js b/lib/stringify.js
index 5f2c845..6079671 100644
--- a/lib/stringify.js
+++ b/lib/stringify.js
@@ -16,7 +16,7 @@ function stringifyNode(node, custom) {
   } else if (type === "div") {
     return (node.before || "") + value + (node.after || "");
   } else if (Array.isArray(node.nodes)) {
-    buf = stringify(node.nodes);
+    buf = stringify(node.nodes, custom);
     if (type !== "function") {
       return buf;
     }
diff --git a/lib/unit.js b/lib/unit.js
index 884d223..c349661 100644
--- a/lib/unit.js
+++ b/lib/unit.js
@@ -4,46 +4,117 @@ var dot = ".".charCodeAt(0);
 var exp = "e".charCodeAt(0);
 var EXP = "E".charCodeAt(0);
 
+// Check if three code points would start a number
+// https://www.w3.org/TR/css-syntax-3/#starts-with-a-number
+function likeNumber(value) {
+  var code = value.charCodeAt(0);
+  var nextCode;
+
+  if (code === plus || code === minus) {
+    nextCode = value.charCodeAt(1);
+
+    if (nextCode >= 48 && nextCode <= 57) {
+      return true;
+    }
+
+    var nextNextCode = value.charCodeAt(2);
+
+    if (nextCode === dot && nextNextCode >= 48 && nextNextCode <= 57) {
+      return true;
+    }
+
+    return false;
+  }
+
+  if (code === dot) {
+    nextCode = value.charCodeAt(1);
+
+    if (nextCode >= 48 && nextCode <= 57) {
+      return true;
+    }
+
+    return false;
+  }
+
+  if (code >= 48 && code <= 57) {
+    return true;
+  }
+
+  return false;
+}
+
+// Consume a number
+// https://www.w3.org/TR/css-syntax-3/#consume-number
 module.exports = function(value) {
   var pos = 0;
   var length = value.length;
-  var dotted = false;
-  var sciPos = -1;
-  var containsNumber = false;
   var code;
+  var nextCode;
+  var nextNextCode;
+
+  if (length === 0 || !likeNumber(value)) {
+    return false;
+  }
+
+  code = value.charCodeAt(pos);
+
+  if (code === plus || code === minus) {
+    pos++;
+  }
 
   while (pos < length) {
     code = value.charCodeAt(pos);
 
-    if (code >= 48 && code <= 57) {
-      containsNumber = true;
-    } else if (code === exp || code === EXP) {
-      if (sciPos > -1 || pos === 0) {
-        break;
-      }
-      sciPos = pos;
-    } else if (code === dot) {
-      if (dotted) {
-        break;
-      }
-      dotted = true;
-    } else if (code === plus || code === minus) {
-      if (pos !== 0) {
-        break;
-      }
-    } else {
+    if (code < 48 || code > 57) {
       break;
     }
 
     pos += 1;
   }
 
-  if (sciPos + 1 === pos) pos--;
+  code = value.charCodeAt(pos);
+  nextCode = value.charCodeAt(pos + 1);
+
+  if (code === dot && nextCode >= 48 && nextCode <= 57) {
+    pos += 2;
+
+    while (pos < length) {
+      code = value.charCodeAt(pos);
+
+      if (code < 48 || code > 57) {
+        break;
+      }
+
+      pos += 1;
+    }
+  }
+
+  code = value.charCodeAt(pos);
+  nextCode = value.charCodeAt(pos + 1);
+  nextNextCode = value.charCodeAt(pos + 2);
+
+  if (
+    (code === exp || code === EXP) &&
+    ((nextCode >= 48 && nextCode <= 57) ||
+      ((nextCode === plus || nextCode === minus) &&
+        nextNextCode >= 48 &&
+        nextNextCode <= 57))
+  ) {
+    pos += nextCode === plus || nextCode === minus ? 3 : 2;
+
+    while (pos < length) {
+      code = value.charCodeAt(pos);
 
-  return containsNumber
-    ? {
-        number: value.slice(0, pos),
-        unit: value.slice(pos)
+      if (code < 48 || code > 57) {
+        break;
       }
-    : false;
+
+      pos += 1;
+    }
+  }
+
+  return {
+    number: value.slice(0, pos),
+    unit: value.slice(pos)
+  };
 };
diff --git a/package.json b/package.json
index 35122da..02d744a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "postcss-value-parser",
-  "version": "4.0.0",
+  "version": "4.2.0",
   "description": "Transforms css values and at-rule params into the tree",
   "main": "lib/index.js",
   "files": [
@@ -15,7 +15,7 @@
     "tape": "^4.10.2"
   },
   "scripts": {
-    "lint:prettier": "prettier '**/*.js' --list-different",
+    "lint:prettier": "prettier \"**/*.js\" \"**/*.ts\" --list-different",
     "lint:js": "eslint . --cache",
     "lint": "yarn lint:js && yarn lint:prettier",
     "pretest": "yarn lint",
diff --git a/test/index.js b/test/index.js
index 7478f9a..ba356d8 100644
--- a/test/index.js
+++ b/test/index.js
@@ -38,6 +38,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 0,
+          sourceEndIndex: 5,
           value: "fn",
           before: " ",
           after: "",
@@ -46,6 +47,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 6,
+          sourceEndIndex: 17,
           value: "fn2",
           before: " ",
           after: "",
@@ -53,6 +55,7 @@ test("ValueParser", function(tp) {
             {
               type: "function",
               sourceIndex: 11,
+              sourceEndIndex: 16,
               value: "fn3",
               before: "",
               after: "",
@@ -63,6 +66,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 11,
+          sourceEndIndex: 16,
           value: "fn3",
           before: "",
           after: "",
@@ -90,6 +94,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 0,
+          sourceEndIndex: 5,
           value: "fn",
           before: " ",
           after: "",
@@ -98,6 +103,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 6,
+          sourceEndIndex: 17,
           value: "fn2",
           before: " ",
           after: "",
@@ -105,6 +111,7 @@ test("ValueParser", function(tp) {
             {
               type: "function",
               sourceIndex: 11,
+              sourceEndIndex: 16,
               value: "fn3",
               before: "",
               after: "",
@@ -131,15 +138,17 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 0,
+          sourceEndIndex: 5,
           value: "fn",
           before: " ",
           after: "",
           nodes: []
         },
-        { type: "space", sourceIndex: 5, value: " " },
+        { type: "space", sourceIndex: 5, sourceEndIndex: 6, value: " " },
         {
           type: "word",
           sourceIndex: 6,
+          sourceEndIndex: 17,
           value: "fn2",
           before: " ",
           after: "",
@@ -147,6 +156,7 @@ test("ValueParser", function(tp) {
             {
               type: "function",
               sourceIndex: 11,
+              sourceEndIndex: 16,
               value: "fn3",
               before: "",
               after: "",
@@ -172,6 +182,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 5,
+          sourceEndIndex: 10,
           value: "fn3",
           before: "",
           after: "",
@@ -180,6 +191,7 @@ test("ValueParser", function(tp) {
         {
           type: "function",
           sourceIndex: 0,
+          sourceEndIndex: 11,
           value: "fn2",
           before: " ",
           after: "",
@@ -187,6 +199,7 @@ test("ValueParser", function(tp) {
             {
               type: "function",
               sourceIndex: 5,
+              sourceEndIndex: 10,
               value: "fn3",
               before: "",
               after: "",
diff --git a/test/parse.js b/test/parse.js
index 5cd41e0..384e783 100644
--- a/test/parse.js
+++ b/test/parse.js
@@ -10,25 +10,31 @@ var tests = [
   {
     message: "should process escaped parentheses (open)",
     fixture: "\\(",
-    expected: [{ type: "word", sourceIndex: 0, value: "\\(" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 2, value: "\\(" }
+    ]
   },
   {
     message: "should process escaped parentheses (close)",
     fixture: "\\)",
-    expected: [{ type: "word", sourceIndex: 0, value: "\\)" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 2, value: "\\)" }
+    ]
   },
   {
     message: "should process escaped parentheses (both)",
     fixture: "\\(\\)",
-    expected: [{ type: "word", sourceIndex: 0, value: "\\(\\)" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 4, value: "\\(\\)" }
+    ]
   },
   {
     message: "should process escaped parentheses (both)",
     fixture: "\\( \\)",
     expected: [
-      { type: "word", sourceIndex: 0, value: "\\(" },
-      { type: "space", sourceIndex: 2, value: " " },
-      { type: "word", sourceIndex: 3, value: "\\)" }
+      { type: "word", sourceIndex: 0, sourceEndIndex: 2, value: "\\(" },
+      { type: "space", sourceIndex: 2, sourceEndIndex: 3, value: " " },
+      { type: "word", sourceIndex: 3, sourceEndIndex: 5, value: "\\)" }
     ]
   },
   {
@@ -38,13 +44,14 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 2,
         value: "",
         before: "",
         after: "",
         nodes: []
       },
-      { type: "space", sourceIndex: 2, value: " " },
-      { type: "word", sourceIndex: 3, value: ")wo)rd)" }
+      { type: "space", sourceIndex: 2, sourceEndIndex: 3, value: " " },
+      { type: "word", sourceIndex: 3, sourceEndIndex: 10, value: ")wo)rd)" }
     ]
   },
   {
@@ -54,6 +61,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 3,
         value: "",
         before: " ",
         after: "",
@@ -68,10 +76,11 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 5,
         value: "",
         before: " ",
         after: " ",
-        nodes: [{ type: "word", sourceIndex: 2, value: "|" }]
+        nodes: [{ type: "word", sourceIndex: 2, sourceEndIndex: 3, value: "|" }]
       }
     ]
   },
@@ -82,6 +91,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 6,
         value: "name",
         before: "",
         after: "",
@@ -96,6 +106,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 6,
         value: "",
         before: "",
         after: "",
@@ -103,6 +114,7 @@ var tests = [
           {
             type: "function",
             sourceIndex: 1,
+            sourceEndIndex: 5,
             value: "",
             before: "",
             after: "",
@@ -110,6 +122,7 @@ var tests = [
               {
                 type: "function",
                 sourceIndex: 2,
+                sourceEndIndex: 4,
                 value: "",
                 before: "",
                 after: "",
@@ -128,6 +141,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 13,
         value: "",
         before: " ",
         after: "",
@@ -135,6 +149,7 @@ var tests = [
           {
             type: "function",
             sourceIndex: 2,
+            sourceEndIndex: 12,
             value: "calc",
             before: "",
             after: " ",
@@ -142,6 +157,7 @@ var tests = [
               {
                 type: "function",
                 sourceIndex: 7,
+                sourceEndIndex: 10,
                 value: "",
                 before: " ",
                 after: "",
@@ -151,35 +167,63 @@ var tests = [
           }
         ]
       },
-      { type: "word", sourceIndex: 13, value: "word" }
+      { type: "word", sourceIndex: 13, sourceEndIndex: 17, value: "word" }
     ]
   },
   {
     message: "should process divider (/)",
     fixture: "/",
     expected: [
-      { type: "div", sourceIndex: 0, value: "/", before: "", after: "" }
+      {
+        type: "div",
+        sourceIndex: 0,
+        sourceEndIndex: 1,
+        value: "/",
+        before: "",
+        after: ""
+      }
     ]
   },
   {
     message: "should process divider (:)",
     fixture: ":",
     expected: [
-      { type: "div", sourceIndex: 0, value: ":", before: "", after: "" }
+      {
+        type: "div",
+        sourceIndex: 0,
+        sourceEndIndex: 1,
+        value: ":",
+        before: "",
+        after: ""
+      }
     ]
   },
   {
     message: "should process divider (,)",
     fixture: ",",
     expected: [
-      { type: "div", sourceIndex: 0, value: ",", before: "", after: "" }
+      {
+        type: "div",
+        sourceIndex: 0,
+        sourceEndIndex: 1,
+        value: ",",
+        before: "",
+        after: ""
+      }
     ]
   },
   {
     message: "should process complex divider",
     fixture: " , ",
     expected: [
-      { type: "div", sourceIndex: 0, value: ",", before: " ", after: " " }
+      {
+        type: "div",
+        sourceIndex: 0,
+        sourceEndIndex: 3,
+        value: ",",
+        before: " ",
+        after: " "
+      }
     ]
   },
   {
@@ -189,6 +233,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 5,
         value: "",
         before: " ",
         after: " ",
@@ -196,6 +241,7 @@ var tests = [
           {
             type: "div",
             sourceIndex: 2,
+            sourceEndIndex: 3,
             value: ",",
             before: "",
             after: ""
@@ -211,49 +257,97 @@ var tests = [
       {
         type: "div",
         sourceIndex: 0,
+        sourceEndIndex: 3,
         value: ",",
         before: " ",
         after: " "
       },
-      { type: "div", sourceIndex: 3, value: ":", before: "", after: " " }
+      {
+        type: "div",
+        sourceIndex: 3,
+        sourceEndIndex: 5,
+        value: ":",
+        before: "",
+        after: " "
+      }
     ]
   },
   {
     message: 'should process empty quoted strings (")',
     fixture: '""',
-    expected: [{ type: "string", sourceIndex: 0, value: "", quote: '"' }]
+    expected: [
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 2,
+        value: "",
+        quote: '"'
+      }
+    ]
   },
   {
     message: "should process empty quoted strings (')",
     fixture: "''",
-    expected: [{ type: "string", sourceIndex: 0, value: "", quote: "'" }]
+    expected: [
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 2,
+        value: "",
+        quote: "'"
+      }
+    ]
   },
   {
     message: "should process escaped quotes (')",
     fixture: "'word\\'word'",
     expected: [
-      { type: "string", sourceIndex: 0, value: "word\\'word", quote: "'" }
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 12,
+        value: "word\\'word",
+        quote: "'"
+      }
     ]
   },
   {
     message: "should process escaped quotes (')",
     fixture: '"word\\"word"',
     expected: [
-      { type: "string", sourceIndex: 0, value: 'word\\"word', quote: '"' }
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 12,
+        value: 'word\\"word',
+        quote: '"'
+      }
     ]
   },
   {
     message: "should process single quotes inside double quotes (')",
     fixture: '"word\'word"',
     expected: [
-      { type: "string", sourceIndex: 0, value: "word'word", quote: '"' }
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: "word'word",
+        quote: '"'
+      }
     ]
   },
   {
     message: "should process double quotes inside single quotes (')",
     fixture: "'word\"word'",
     expected: [
-      { type: "string", sourceIndex: 0, value: 'word"word', quote: "'" }
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: 'word"word',
+        quote: "'"
+      }
     ]
   },
   {
@@ -263,6 +357,7 @@ var tests = [
       {
         type: "string",
         sourceIndex: 0,
+        sourceEndIndex: 5,
         value: "word",
         quote: '"',
         unclosed: true
@@ -276,6 +371,7 @@ var tests = [
       {
         type: "string",
         sourceIndex: 0,
+        sourceEndIndex: 6,
         value: "word\\",
         quote: '"',
         unclosed: true
@@ -285,33 +381,58 @@ var tests = [
   {
     message: "should process quoted strings",
     fixture: '"string"',
-    expected: [{ type: "string", sourceIndex: 0, value: "string", quote: '"' }]
+    expected: [
+      {
+        type: "string",
+        sourceIndex: 0,
+        sourceEndIndex: 8,
+        value: "string",
+        quote: '"'
+      }
+    ]
   },
   {
     message: "should process quoted strings and words",
     fixture: 'word1"string"word2',
     expected: [
-      { type: "word", sourceIndex: 0, value: "word1" },
-      { type: "string", sourceIndex: 5, value: "string", quote: '"' },
-      { type: "word", sourceIndex: 13, value: "word2" }
+      { type: "word", sourceIndex: 0, sourceEndIndex: 5, value: "word1" },
+      {
+        type: "string",
+        sourceIndex: 5,
+        sourceEndIndex: 13,
+        value: "string",
+        quote: '"'
+      },
+      { type: "word", sourceIndex: 13, sourceEndIndex: 18, value: "word2" }
     ]
   },
   {
     message: "should process quoted strings and spaces",
     fixture: ' "string" ',
     expected: [
-      { type: "space", sourceIndex: 0, value: " " },
-      { type: "string", sourceIndex: 1, value: "string", quote: '"' },
-      { type: "space", sourceIndex: 9, value: " " }
+      { type: "space", sourceIndex: 0, sourceEndIndex: 1, value: " " },
+      {
+        type: "string",
+        sourceIndex: 1,
+        sourceEndIndex: 9,
+        value: "string",
+        quote: '"'
+      },
+      { type: "space", sourceIndex: 9, sourceEndIndex: 10, value: " " }
     ]
   },
   {
     message: "should process escaped symbols as words",
     fixture: " \\\"word\\'\\ \\\t ",
     expected: [
-      { type: "space", sourceIndex: 0, value: " " },
-      { type: "word", sourceIndex: 1, value: "\\\"word\\'\\ \\\t" },
-      { type: "space", sourceIndex: 13, value: " " }
+      { type: "space", sourceIndex: 0, sourceEndIndex: 1, value: " " },
+      {
+        type: "word",
+        sourceIndex: 1,
+        sourceEndIndex: 13,
+        value: "\\\"word\\'\\ \\\t"
+      },
+      { type: "space", sourceIndex: 13, sourceEndIndex: 14, value: " " }
     ]
   },
   {
@@ -319,32 +440,41 @@ var tests = [
     fixture:
       "bold italic 12px \t /3 'Open Sans', Arial, \"Helvetica Neue\", sans-serif",
     expected: [
-      { type: "word", sourceIndex: 0, value: "bold" },
-      { type: "space", sourceIndex: 4, value: " " },
-      { type: "word", sourceIndex: 5, value: "italic" },
-      { type: "space", sourceIndex: 11, value: " " },
-      { type: "word", sourceIndex: 12, value: "12px" },
+      { type: "word", sourceIndex: 0, sourceEndIndex: 4, value: "bold" },
+      { type: "space", sourceIndex: 4, sourceEndIndex: 5, value: " " },
+      { type: "word", sourceIndex: 5, sourceEndIndex: 11, value: "italic" },
+      { type: "space", sourceIndex: 11, sourceEndIndex: 12, value: " " },
+      { type: "word", sourceIndex: 12, sourceEndIndex: 16, value: "12px" },
       {
         type: "div",
         sourceIndex: 16,
+        sourceEndIndex: 20,
         value: "/",
         before: " \t ",
         after: ""
       },
-      { type: "word", sourceIndex: 20, value: "3" },
-      { type: "space", sourceIndex: 21, value: " " },
-      { type: "string", sourceIndex: 22, value: "Open Sans", quote: "'" },
+      { type: "word", sourceIndex: 20, sourceEndIndex: 21, value: "3" },
+      { type: "space", sourceIndex: 21, sourceEndIndex: 22, value: " " },
+      {
+        type: "string",
+        sourceIndex: 22,
+        sourceEndIndex: 33,
+        value: "Open Sans",
+        quote: "'"
+      },
       {
         type: "div",
         sourceIndex: 33,
+        sourceEndIndex: 35,
         value: ",",
         before: "",
         after: " "
       },
-      { type: "word", sourceIndex: 35, value: "Arial" },
+      { type: "word", sourceIndex: 35, sourceEndIndex: 40, value: "Arial" },
       {
         type: "div",
         sourceIndex: 40,
+        sourceEndIndex: 42,
         value: ",",
         before: "",
         after: " "
@@ -352,17 +482,19 @@ var tests = [
       {
         type: "string",
         sourceIndex: 42,
+        sourceEndIndex: 58,
         value: "Helvetica Neue",
         quote: '"'
       },
       {
         type: "div",
         sourceIndex: 58,
+        sourceEndIndex: 60,
         value: ",",
         before: "",
         after: " "
       },
-      { type: "word", sourceIndex: 60, value: "sans-serif" }
+      { type: "word", sourceIndex: 60, sourceEndIndex: 70, value: "sans-serif" }
     ]
   },
   {
@@ -372,27 +504,30 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 20,
         value: "rgba",
         before: " ",
         after: " ",
         nodes: [
-          { type: "word", sourceIndex: 6, value: "29" },
+          { type: "word", sourceIndex: 6, sourceEndIndex: 8, value: "29" },
           {
             type: "div",
             sourceIndex: 8,
+            sourceEndIndex: 10,
             value: ",",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 10, value: "439" },
+          { type: "word", sourceIndex: 10, sourceEndIndex: 13, value: "439" },
           {
             type: "div",
             sourceIndex: 13,
+            sourceEndIndex: 16,
             value: ",",
             before: " ",
             after: " "
           },
-          { type: "word", sourceIndex: 16, value: "29" }
+          { type: "word", sourceIndex: 16, sourceEndIndex: 18, value: "29" }
         ]
       }
     ]
@@ -404,10 +539,18 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 22,
         value: "url",
         before: " ",
         after: " ",
-        nodes: [{ type: "word", sourceIndex: 5, value: "/gfx/img/bg.jpg" }]
+        nodes: [
+          {
+            type: "word",
+            sourceIndex: 5,
+            sourceEndIndex: 20,
+            value: "/gfx/img/bg.jpg"
+          }
+        ]
       }
     ]
   },
@@ -418,13 +561,19 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 21,
         value: "url",
         before: " ",
         after: "",
         unclosed: true,
         nodes: [
-          { type: "word", sourceIndex: 5, value: "/gfx/img/bg.jpg" },
-          { type: "space", sourceIndex: 20, value: " " }
+          {
+            type: "word",
+            sourceIndex: 5,
+            sourceEndIndex: 20,
+            value: "/gfx/img/bg.jpg"
+          },
+          { type: "space", sourceIndex: 20, sourceEndIndex: 21, value: " " }
         ]
       }
     ]
@@ -436,6 +585,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 30,
         value: "url",
         before: " ",
         after: " ",
@@ -443,11 +593,12 @@ var tests = [
           {
             type: "string",
             sourceIndex: 5,
+            sourceEndIndex: 22,
             quote: '"',
             value: "/gfx/img/bg.jpg"
           },
-          { type: "space", sourceIndex: 22, value: " " },
-          { type: "word", sourceIndex: 23, value: "hello" }
+          { type: "space", sourceIndex: 22, sourceEndIndex: 23, value: " " },
+          { type: "word", sourceIndex: 23, sourceEndIndex: 28, value: "hello" }
         ]
       }
     ]
@@ -459,6 +610,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 11,
         value: "calc",
         before: "",
         after: "",
@@ -466,26 +618,77 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 6,
             value: "1"
           },
           {
             type: "space",
             sourceIndex: 6,
+            sourceEndIndex: 7,
             value: " "
           },
           {
             type: "word",
             sourceIndex: 7,
+            sourceEndIndex: 8,
             value: "+"
           },
           {
             type: "space",
             sourceIndex: 8,
+            sourceEndIndex: 9,
             value: " "
           },
           {
             type: "word",
             sourceIndex: 9,
+            sourceEndIndex: 10,
+            value: "2"
+          }
+        ]
+      }
+    ]
+  },
+  {
+    message: "should correctly parse subtraction with spaces",
+    fixture: "calc(1 - 2)",
+    expected: [
+      {
+        type: "function",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: "calc",
+        before: "",
+        after: "",
+        nodes: [
+          {
+            type: "word",
+            sourceIndex: 5,
+            sourceEndIndex: 6,
+            value: "1"
+          },
+          {
+            type: "space",
+            sourceIndex: 6,
+            sourceEndIndex: 7,
+            value: " "
+          },
+          {
+            type: "word",
+            sourceIndex: 7,
+            sourceEndIndex: 8,
+            value: "-"
+          },
+          {
+            type: "space",
+            sourceIndex: 8,
+            sourceEndIndex: 9,
+            value: " "
+          },
+          {
+            type: "word",
+            sourceIndex: 9,
+            sourceEndIndex: 10,
             value: "2"
           }
         ]
@@ -499,6 +702,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 11,
         value: "calc",
         before: "",
         after: "",
@@ -506,26 +710,77 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 6,
             value: "1"
           },
           {
             type: "space",
             sourceIndex: 6,
+            sourceEndIndex: 7,
             value: " "
           },
           {
             type: "word",
             sourceIndex: 7,
+            sourceEndIndex: 8,
             value: "*"
           },
           {
             type: "space",
             sourceIndex: 8,
+            sourceEndIndex: 9,
+            value: " "
+          },
+          {
+            type: "word",
+            sourceIndex: 9,
+            sourceEndIndex: 10,
+            value: "2"
+          }
+        ]
+      }
+    ]
+  },
+  {
+    message: "should correctly parse division with spaces",
+    fixture: "calc(1 / 2)",
+    expected: [
+      {
+        type: "function",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: "calc",
+        before: "",
+        after: "",
+        nodes: [
+          {
+            type: "word",
+            sourceIndex: 5,
+            sourceEndIndex: 6,
+            value: "1"
+          },
+          {
+            type: "space",
+            sourceIndex: 6,
+            sourceEndIndex: 7,
+            value: " "
+          },
+          {
+            type: "word",
+            sourceIndex: 7,
+            sourceEndIndex: 8,
+            value: "/"
+          },
+          {
+            type: "space",
+            sourceIndex: 8,
+            sourceEndIndex: 9,
             value: " "
           },
           {
             type: "word",
             sourceIndex: 9,
+            sourceEndIndex: 10,
             value: "2"
           }
         ]
@@ -539,6 +794,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 9,
         value: "calc",
         before: "",
         after: "",
@@ -546,16 +802,53 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 6,
             value: "1"
           },
           {
             type: "word",
             sourceIndex: 6,
+            sourceEndIndex: 7,
             value: "*"
           },
           {
             type: "word",
             sourceIndex: 7,
+            sourceEndIndex: 8,
+            value: "2"
+          }
+        ]
+      }
+    ]
+  },
+  {
+    message: "should correctly parse division without spaces",
+    fixture: "calc(1/2)",
+    expected: [
+      {
+        type: "function",
+        sourceIndex: 0,
+        sourceEndIndex: 9,
+        value: "calc",
+        before: "",
+        after: "",
+        nodes: [
+          {
+            type: "word",
+            sourceIndex: 5,
+            sourceEndIndex: 6,
+            value: "1"
+          },
+          {
+            type: "word",
+            sourceIndex: 6,
+            sourceEndIndex: 7,
+            value: "/"
+          },
+          {
+            type: "word",
+            sourceIndex: 7,
+            sourceEndIndex: 8,
             value: "2"
           }
         ]
@@ -569,6 +862,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 34,
         value: "calc",
         before: "",
         after: "",
@@ -576,6 +870,7 @@ var tests = [
           {
             type: "function",
             sourceIndex: 5,
+            sourceEndIndex: 26,
             value: "",
             before: "",
             after: "",
@@ -583,6 +878,7 @@ var tests = [
               {
                 type: "function",
                 sourceIndex: 6,
+                sourceEndIndex: 21,
                 value: "",
                 before: "",
                 after: "",
@@ -590,26 +886,31 @@ var tests = [
                   {
                     type: "word",
                     sourceIndex: 7,
+                    sourceEndIndex: 12,
                     value: "768px"
                   },
                   {
                     type: "space",
                     sourceIndex: 12,
+                    sourceEndIndex: 13,
                     value: " "
                   },
                   {
                     type: "word",
                     sourceIndex: 13,
+                    sourceEndIndex: 14,
                     value: "-"
                   },
                   {
                     type: "space",
                     sourceIndex: 14,
+                    sourceEndIndex: 15,
                     value: " "
                   },
                   {
                     type: "word",
                     sourceIndex: 15,
+                    sourceEndIndex: 20,
                     value: "100vw"
                   }
                 ]
@@ -617,17 +918,18 @@ var tests = [
               {
                 type: "div",
                 sourceIndex: 21,
+                sourceEndIndex: 24,
                 value: "/",
                 before: " ",
                 after: " "
               },
-              { type: "word", sourceIndex: 24, value: "2" }
+              { type: "word", sourceIndex: 24, sourceEndIndex: 25, value: "2" }
             ]
           },
-          { type: "space", sourceIndex: 26, value: " " },
-          { type: "word", sourceIndex: 27, value: "-" },
-          { type: "space", sourceIndex: 28, value: " " },
-          { type: "word", sourceIndex: 29, value: "15px" }
+          { type: "space", sourceIndex: 26, sourceEndIndex: 27, value: " " },
+          { type: "word", sourceIndex: 27, sourceEndIndex: 28, value: "-" },
+          { type: "space", sourceIndex: 28, sourceEndIndex: 29, value: " " },
+          { type: "word", sourceIndex: 29, sourceEndIndex: 33, value: "15px" }
         ]
       }
     ]
@@ -639,40 +941,59 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 18,
         value: "",
         before: "",
         after: "",
         nodes: [
-          { type: "word", sourceIndex: 1, value: "min-width" },
+          {
+            type: "word",
+            sourceIndex: 1,
+            sourceEndIndex: 10,
+            value: "min-width"
+          },
           {
             type: "div",
             sourceIndex: 10,
+            sourceEndIndex: 12,
             value: ":",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 12, value: "700px" }
+          { type: "word", sourceIndex: 12, sourceEndIndex: 17, value: "700px" }
         ]
       },
-      { type: "space", sourceIndex: 18, value: " " },
-      { type: "word", sourceIndex: 19, value: "and" },
-      { type: "space", sourceIndex: 22, value: " " },
+      { type: "space", sourceIndex: 18, sourceEndIndex: 19, value: " " },
+      { type: "word", sourceIndex: 19, sourceEndIndex: 22, value: "and" },
+      { type: "space", sourceIndex: 22, sourceEndIndex: 23, value: " " },
       {
         type: "function",
         sourceIndex: 23,
+        sourceEndIndex: 49,
         value: "",
         before: "",
         after: "",
         nodes: [
-          { type: "word", sourceIndex: 24, value: "orientation" },
+          {
+            type: "word",
+            sourceIndex: 24,
+            sourceEndIndex: 35,
+            value: "orientation"
+          },
           {
             type: "div",
             sourceIndex: 35,
+            sourceEndIndex: 37,
             value: ":",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 37, value: "\\$landscape" }
+          {
+            type: "word",
+            sourceIndex: 37,
+            sourceEndIndex: 48,
+            value: "\\$landscape"
+          }
         ]
       }
     ]
@@ -684,6 +1005,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 39,
         value: "url",
         before: " ",
         after: " ",
@@ -691,6 +1013,7 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 37,
             value: "http://website.com/assets\\)_test"
           }
         ]
@@ -704,6 +1027,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 22,
         value: "fn1",
         before: "",
         after: "",
@@ -711,14 +1035,18 @@ var tests = [
           {
             type: "function",
             sourceIndex: 4,
+            sourceEndIndex: 12,
             value: "fn2",
             before: "",
             after: "",
-            nodes: [{ type: "word", sourceIndex: 8, value: "255" }]
+            nodes: [
+              { type: "word", sourceIndex: 8, sourceEndIndex: 11, value: "255" }
+            ]
           },
           {
             type: "div",
             sourceIndex: 12,
+            sourceEndIndex: 14,
             value: ",",
             before: "",
             after: " "
@@ -726,16 +1054,20 @@ var tests = [
           {
             type: "function",
             sourceIndex: 14,
+            sourceEndIndex: 21,
             value: "fn3",
             before: "",
             after: "",
-            nodes: [{ type: "word", sourceIndex: 18, value: ".2" }]
+            nodes: [
+              { type: "word", sourceIndex: 18, sourceEndIndex: 20, value: ".2" }
+            ]
           }
         ]
       },
       {
         type: "div",
         sourceIndex: 22,
+        sourceEndIndex: 24,
         value: ",",
         before: "",
         after: " "
@@ -743,6 +1075,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 24,
+        sourceEndIndex: 45,
         value: "fn4",
         before: "",
         after: "",
@@ -750,29 +1083,37 @@ var tests = [
           {
             type: "function",
             sourceIndex: 28,
+            sourceEndIndex: 39,
             value: "fn5",
             before: "",
             after: "",
             nodes: [
-              { type: "word", sourceIndex: 32, value: "255" },
+              {
+                type: "word",
+                sourceIndex: 32,
+                sourceEndIndex: 35,
+                value: "255"
+              },
               {
                 type: "div",
                 sourceIndex: 35,
+                sourceEndIndex: 36,
                 value: ",",
                 before: "",
                 after: ""
               },
-              { type: "word", sourceIndex: 36, value: ".2" }
+              { type: "word", sourceIndex: 36, sourceEndIndex: 38, value: ".2" }
             ]
           },
           {
             type: "div",
             sourceIndex: 39,
+            sourceEndIndex: 41,
             value: ",",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 41, value: "fn6" }
+          { type: "word", sourceIndex: 41, sourceEndIndex: 44, value: "fn6" }
         ]
       }
     ]
@@ -784,17 +1125,18 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 11,
         value: "",
         before: "",
         after: "",
         unclosed: true,
         nodes: [
-          { type: "word", sourceIndex: 1, value: "0" },
-          { type: "space", sourceIndex: 2, value: " " },
-          { type: "word", sourceIndex: 3, value: "32" },
-          { type: "space", sourceIndex: 5, value: " " },
-          { type: "word", sourceIndex: 6, value: "word" },
-          { type: "space", sourceIndex: 10, value: " " }
+          { type: "word", sourceIndex: 1, sourceEndIndex: 2, value: "0" },
+          { type: "space", sourceIndex: 2, sourceEndIndex: 3, value: " " },
+          { type: "word", sourceIndex: 3, sourceEndIndex: 5, value: "32" },
+          { type: "space", sourceIndex: 5, sourceEndIndex: 6, value: " " },
+          { type: "word", sourceIndex: 6, sourceEndIndex: 10, value: "word" },
+          { type: "space", sourceIndex: 10, sourceEndIndex: 11, value: " " }
         ]
       }
     ]
@@ -806,6 +1148,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 8,
         value: "",
         before: " ",
         after: "",
@@ -814,6 +1157,7 @@ var tests = [
           {
             type: "function",
             sourceIndex: 2,
+            sourceEndIndex: 8,
             value: "",
             before: " ",
             after: "",
@@ -822,12 +1166,13 @@ var tests = [
               {
                 type: "function",
                 sourceIndex: 4,
+                sourceEndIndex: 7,
                 value: "",
                 before: " ",
                 after: "",
                 nodes: []
               },
-              { type: "space", sourceIndex: 7, value: " " }
+              { type: "space", sourceIndex: 7, sourceEndIndex: 8, value: " " }
             ]
           }
         ]
@@ -838,20 +1183,22 @@ var tests = [
     message: "shouldn't throw an error on unopened function",
     fixture: "0 32 word ) ",
     expected: [
-      { type: "word", sourceIndex: 0, value: "0" },
-      { type: "space", sourceIndex: 1, value: " " },
-      { type: "word", sourceIndex: 2, value: "32" },
-      { type: "space", sourceIndex: 4, value: " " },
-      { type: "word", sourceIndex: 5, value: "word" },
-      { type: "space", sourceIndex: 9, value: " " },
-      { type: "word", sourceIndex: 10, value: ")" },
-      { type: "space", sourceIndex: 11, value: " " }
+      { type: "word", sourceIndex: 0, sourceEndIndex: 1, value: "0" },
+      { type: "space", sourceIndex: 1, sourceEndIndex: 2, value: " " },
+      { type: "word", sourceIndex: 2, sourceEndIndex: 4, value: "32" },
+      { type: "space", sourceIndex: 4, sourceEndIndex: 5, value: " " },
+      { type: "word", sourceIndex: 5, sourceEndIndex: 9, value: "word" },
+      { type: "space", sourceIndex: 9, sourceEndIndex: 10, value: " " },
+      { type: "word", sourceIndex: 10, sourceEndIndex: 11, value: ")" },
+      { type: "space", sourceIndex: 11, sourceEndIndex: 12, value: " " }
     ]
   },
   {
     message: "should process escaped spaces as word in fonts",
     fixture: "Bond\\ 007",
-    expected: [{ type: "word", sourceIndex: 0, value: "Bond\\ 007" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 9, value: "Bond\\ 007" }
+    ]
   },
   {
     message: "should parse double url and comma",
@@ -860,14 +1207,23 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 16,
         value: "url",
         before: "",
         after: "",
-        nodes: [{ type: "word", sourceIndex: 4, value: "foo/bar.jpg" }]
+        nodes: [
+          {
+            type: "word",
+            sourceIndex: 4,
+            sourceEndIndex: 15,
+            value: "foo/bar.jpg"
+          }
+        ]
       },
       {
         type: "div",
         sourceIndex: 16,
+        sourceEndIndex: 18,
         value: ",",
         before: "",
         after: " "
@@ -875,6 +1231,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 18,
+        sourceEndIndex: 49,
         value: "url",
         before: "",
         after: "",
@@ -882,6 +1239,7 @@ var tests = [
           {
             type: "word",
             sourceIndex: 22,
+            sourceEndIndex: 48,
             value: "http://website.com/img.jpg"
           }
         ]
@@ -895,6 +1253,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 5,
         value: "url",
         before: "",
         after: "",
@@ -909,6 +1268,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 6,
         value: "url",
         before: " ",
         after: "",
@@ -923,6 +1283,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 8,
         value: "url",
         before: "   ",
         after: "",
@@ -937,6 +1298,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 6,
         value: "url",
         before: "\n",
         after: "",
@@ -951,6 +1313,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 7,
         value: "url",
         before: "\r\n",
         after: "",
@@ -965,6 +1328,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 8,
         value: "url",
         before: "\n\n\n",
         after: "",
@@ -979,6 +1343,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 11,
         value: "url",
         before: "\r\n\r\n\r\n",
         after: "",
@@ -993,6 +1358,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 16,
         value: "url",
         before: "  \n \t  \r\n  ",
         after: "",
@@ -1004,15 +1370,20 @@ var tests = [
     message: "should parse comments",
     fixture: "/*before*/ 1px /*between*/ 1px /*after*/",
     expected: [
-      { type: "comment", sourceIndex: 0, value: "before" },
-      { type: "space", sourceIndex: 10, value: " " },
-      { type: "word", sourceIndex: 11, value: "1px" },
-      { type: "space", sourceIndex: 14, value: " " },
-      { type: "comment", sourceIndex: 15, value: "between" },
-      { type: "space", sourceIndex: 26, value: " " },
-      { type: "word", sourceIndex: 27, value: "1px" },
-      { type: "space", sourceIndex: 30, value: " " },
-      { type: "comment", sourceIndex: 31, value: "after" }
+      { type: "comment", sourceIndex: 0, sourceEndIndex: 10, value: "before" },
+      { type: "space", sourceIndex: 10, sourceEndIndex: 11, value: " " },
+      { type: "word", sourceIndex: 11, sourceEndIndex: 14, value: "1px" },
+      { type: "space", sourceIndex: 14, sourceEndIndex: 15, value: " " },
+      {
+        type: "comment",
+        sourceIndex: 15,
+        sourceEndIndex: 26,
+        value: "between"
+      },
+      { type: "space", sourceIndex: 26, sourceEndIndex: 27, value: " " },
+      { type: "word", sourceIndex: 27, sourceEndIndex: 30, value: "1px" },
+      { type: "space", sourceIndex: 30, sourceEndIndex: 31, value: " " },
+      { type: "comment", sourceIndex: 31, sourceEndIndex: 40, value: "after" }
     ]
   },
   {
@@ -1022,36 +1393,40 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 26,
         value: "rgba",
         before: " ",
         after: " ",
         nodes: [
-          { type: "word", sourceIndex: 6, value: "0" },
+          { type: "word", sourceIndex: 6, sourceEndIndex: 7, value: "0" },
           {
             type: "div",
             sourceIndex: 7,
+            sourceEndIndex: 9,
             value: ",",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 9, value: "55" },
+          { type: "word", sourceIndex: 9, sourceEndIndex: 11, value: "55" },
           {
             type: "div",
             sourceIndex: 11,
+            sourceEndIndex: 12,
             value: "/",
             before: "",
             after: ""
           },
-          { type: "word", sourceIndex: 12, value: "55" },
+          { type: "word", sourceIndex: 12, sourceEndIndex: 14, value: "55" },
           {
             type: "div",
             sourceIndex: 14,
+            sourceEndIndex: 16,
             value: ",",
             before: "",
             after: " "
           },
-          { type: "word", sourceIndex: 16, value: "0" },
-          { type: "comment", sourceIndex: 17, value: ",.5" }
+          { type: "word", sourceIndex: 16, sourceEndIndex: 17, value: "0" },
+          { type: "comment", sourceIndex: 17, sourceEndIndex: 24, value: ",.5" }
         ]
       }
     ]
@@ -1064,6 +1439,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 33,
         value: "url",
         before: " ",
         after: " ",
@@ -1071,11 +1447,17 @@ var tests = [
           {
             type: "string",
             sourceIndex: 5,
+            sourceEndIndex: 19,
             value: "/demo/bg.png",
             quote: '"'
           },
-          { type: "space", sourceIndex: 19, value: " " },
-          { type: "comment", sourceIndex: 20, value: "comment" }
+          { type: "space", sourceIndex: 19, sourceEndIndex: 20, value: " " },
+          {
+            type: "comment",
+            sourceIndex: 20,
+            sourceEndIndex: 31,
+            value: "comment"
+          }
         ]
       }
     ]
@@ -1088,6 +1470,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 31,
         value: "url",
         before: " ",
         after: " ",
@@ -1095,6 +1478,7 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 29,
             value: "/*comment*/ /demo/bg.png"
           }
         ]
@@ -1109,6 +1493,7 @@ var tests = [
       {
         type: "function",
         sourceIndex: 0,
+        sourceEndIndex: 31,
         value: "url",
         before: " ",
         after: " ",
@@ -1116,6 +1501,7 @@ var tests = [
           {
             type: "word",
             sourceIndex: 5,
+            sourceEndIndex: 29,
             value: "/demo/bg.png /*comment*/"
           }
         ]
@@ -1126,13 +1512,14 @@ var tests = [
     message: "should parse unclosed comments",
     fixture: "/*comment*/ 1px /* unclosed ",
     expected: [
-      { type: "comment", sourceIndex: 0, value: "comment" },
-      { type: "space", sourceIndex: 11, value: " " },
-      { type: "word", sourceIndex: 12, value: "1px" },
-      { type: "space", sourceIndex: 15, value: " " },
+      { type: "comment", sourceIndex: 0, sourceEndIndex: 11, value: "comment" },
+      { type: "space", sourceIndex: 11, sourceEndIndex: 12, value: " " },
+      { type: "word", sourceIndex: 12, sourceEndIndex: 15, value: "1px" },
+      { type: "space", sourceIndex: 15, sourceEndIndex: 16, value: " " },
       {
         type: "comment",
         sourceIndex: 16,
+        sourceEndIndex: 28,
         value: " unclosed ",
         unclosed: true
       }
@@ -1142,66 +1529,129 @@ var tests = [
     message: "should respect escape character",
     fixture: "Hawaii \\35 -0",
     expected: [
-      { type: "word", sourceIndex: 0, value: "Hawaii" },
-      { type: "space", sourceIndex: 6, value: " " },
-      { type: "word", sourceIndex: 7, value: "\\35" },
-      { type: "space", sourceIndex: 10, value: " " },
-      { type: "word", sourceIndex: 11, value: "-0" }
+      { type: "word", sourceIndex: 0, sourceEndIndex: 6, value: "Hawaii" },
+      { type: "space", sourceIndex: 6, sourceEndIndex: 7, value: " " },
+      { type: "word", sourceIndex: 7, sourceEndIndex: 10, value: "\\35" },
+      { type: "space", sourceIndex: 10, sourceEndIndex: 11, value: " " },
+      { type: "word", sourceIndex: 11, sourceEndIndex: 13, value: "-0" }
     ]
   },
   {
     message: "should parse unicode-range (single codepoint)",
     fixture: "U+26",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "U+26" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 4,
+        value: "U+26"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (single codepoint) 2",
     fixture: "U+0-7F",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "U+0-7F" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 6,
+        value: "U+0-7F"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (single codepoint) 3",
     fixture: "U+0-7f",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "U+0-7f" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 6,
+        value: "U+0-7f"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (single codepoint) (lowercase)",
     fixture: "u+26",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "u+26" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 4,
+        value: "u+26"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (codepoint range)",
     fixture: "U+0025-00FF",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "U+0025-00FF" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: "U+0025-00FF"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (wildcard range)",
     fixture: "U+4??",
-    expected: [{ type: "unicode-range", sourceIndex: 0, value: "U+4??" }]
+    expected: [
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 5,
+        value: "U+4??"
+      }
+    ]
   },
   {
     message: "should parse unicode-range (multiple values)",
     fixture: "U+0025-00FF, U+4??",
     expected: [
-      { type: "unicode-range", sourceIndex: 0, value: "U+0025-00FF" },
-      { type: "div", sourceIndex: 11, value: ",", before: "", after: " " },
-      { type: "unicode-range", sourceIndex: 13, value: "U+4??" }
+      {
+        type: "unicode-range",
+        sourceIndex: 0,
+        sourceEndIndex: 11,
+        value: "U+0025-00FF"
+      },
+      {
+        type: "div",
+        sourceIndex: 11,
+        sourceEndIndex: 13,
+        value: ",",
+        before: "",
+        after: " "
+      },
+      {
+        type: "unicode-range",
+        sourceIndex: 13,
+        sourceEndIndex: 18,
+        value: "U+4??"
+      }
     ]
   },
   {
     message: "should parse invalid unicode-range as word",
     fixture: "U+4??Z",
-    expected: [{ type: "word", sourceIndex: 0, value: "U+4??Z" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 6, value: "U+4??Z" }
+    ]
   },
   {
     message: "should parse invalid unicode-range as word 2",
     fixture: "U+",
-    expected: [{ type: "word", sourceIndex: 0, value: "U+" }]
+    expected: [{ type: "word", sourceIndex: 0, sourceEndIndex: 2, value: "U+" }]
   },
   {
     message: "should parse invalid unicode-range as word 2",
     fixture: "U+Z",
-    expected: [{ type: "word", sourceIndex: 0, value: "U+Z" }]
+    expected: [
+      { type: "word", sourceIndex: 0, sourceEndIndex: 3, value: "U+Z" }
+    ]
   }
 ];
 
diff --git a/test/stringify.js b/test/stringify.js
index fb695a5..36d13f2 100644
--- a/test/stringify.js
+++ b/test/stringify.js
@@ -89,7 +89,7 @@ var tests = [
 ];
 
 test("Stringify", function(t) {
-  t.plan(tests.length + 3);
+  t.plan(tests.length + 4);
 
   tests.forEach(function(opts) {
     t.equal(stringify(parse(opts.fixture)), opts.fixture, opts.message);
@@ -131,4 +131,13 @@ test("Stringify", function(t) {
 
   tokens[1].type = "word";
   t.equal(stringify(tokens), " rgba ", "Shouldn't process nodes of work type");
+
+  t.equal(
+    stringify(parse("calc(1px + var(--bar))"), function(node) {
+      if (node.type === "function" && node.value === "var") {
+        return "10px";
+      }
+    }),
+    "calc(1px + 10px)"
+  );
 });
diff --git a/test/unit.js b/test/unit.js
index 87279ed..35c94e1 100644
--- a/test/unit.js
+++ b/test/unit.js
@@ -12,15 +12,15 @@ var tests = [
   },
   {
     fixture: "2.",
-    expected: { number: "2.", unit: "" }
+    expected: { number: "2", unit: "." }
   },
   {
     fixture: "+2.",
-    expected: { number: "+2.", unit: "" }
+    expected: { number: "+2", unit: "." }
   },
   {
     fixture: "-2.",
-    expected: { number: "-2.", unit: "" }
+    expected: { number: "-2", unit: "." }
   },
   {
     fixture: "+-2.",
@@ -57,6 +57,218 @@ var tests = [
   {
     fixture: "e1",
     expected: false
+  },
+  {
+    fixture: "2rem",
+    expected: { number: "2", unit: "rem" }
+  },
+  {
+    fixture: "2.000rem",
+    expected: { number: "2.000", unit: "rem" }
+  },
+  {
+    fixture: "+2rem",
+    expected: { number: "+2", unit: "rem" }
+  },
+  {
+    fixture: "-2rem",
+    expected: { number: "-2", unit: "rem" }
+  },
+  {
+    fixture: "1.1rem",
+    expected: { number: "1.1", unit: "rem" }
+  },
+  {
+    fixture: "+1.1rem",
+    expected: { number: "+1.1", unit: "rem" }
+  },
+  {
+    fixture: "-1.1rem",
+    expected: { number: "-1.1", unit: "rem" }
+  },
+  {
+    fixture: "1.1e1rem",
+    expected: { number: "1.1e1", unit: "rem" }
+  },
+  {
+    fixture: "+1.1e1rem",
+    expected: { number: "+1.1e1", unit: "rem" }
+  },
+  {
+    fixture: "-1.1e1rem",
+    expected: { number: "-1.1e1", unit: "rem" }
+  },
+  {
+    fixture: "1.1e+1rem",
+    expected: { number: "1.1e+1", unit: "rem" }
+  },
+  {
+    fixture: "1.1e-1rem",
+    expected: { number: "1.1e-1", unit: "rem" }
+  },
+  {
+    fixture: "1.1e1e1rem",
+    expected: { number: "1.1e1", unit: "e1rem" }
+  },
+  {
+    fixture: "1.1e-1e",
+    expected: { number: "1.1e-1", unit: "e" }
+  },
+  {
+    fixture: "1.1e-1rem",
+    expected: { number: "1.1e-1", unit: "rem" }
+  },
+  {
+    fixture: "1.1e--++1e",
+    expected: { number: "1.1", unit: "e--++1e" }
+  },
+  {
+    fixture: "1.1e--++1rem",
+    expected: { number: "1.1", unit: "e--++1rem" }
+  },
+  {
+    fixture: "100+px",
+    expected: { number: "100", unit: "+px" }
+  },
+  {
+    fixture: "100.0.0px",
+    expected: { number: "100.0", unit: ".0px" }
+  },
+  {
+    fixture: "100e1epx",
+    expected: { number: "100e1", unit: "epx" }
+  },
+  {
+    fixture: "100e1e1px",
+    expected: { number: "100e1", unit: "e1px" }
+  },
+  {
+    fixture: "+100.1e+1e+1px",
+    expected: { number: "+100.1e+1", unit: "e+1px" }
+  },
+  {
+    fixture: "-100.1e-1e-1px",
+    expected: { number: "-100.1e-1", unit: "e-1px" }
+  },
+  {
+    fixture: ".5px",
+    expected: { number: ".5", unit: "px" }
+  },
+  {
+    fixture: "+.5px",
+    expected: { number: "+.5", unit: "px" }
+  },
+  {
+    fixture: "-.5px",
+    expected: { number: "-.5", unit: "px" }
+  },
+  {
+    fixture: ".5e1px",
+    expected: { number: ".5e1", unit: "px" }
+  },
+  {
+    fixture: "-.5e1px",
+    expected: { number: "-.5e1", unit: "px" }
+  },
+  {
+    fixture: "+.5e1px",
+    expected: { number: "+.5e1", unit: "px" }
+  },
+  {
+    fixture: ".5e1e1px",
+    expected: { number: ".5e1", unit: "e1px" }
+  },
+  {
+    fixture: ".5.5px",
+    expected: { number: ".5", unit: ".5px" }
+  },
+  {
+    fixture: "1e",
+    expected: { number: "1", unit: "e" }
+  },
+  {
+    fixture: "1e1",
+    expected: { number: "1e1", unit: "" }
+  },
+  {
+    fixture: "1ee",
+    expected: { number: "1", unit: "ee" }
+  },
+  {
+    fixture: "1e+",
+    expected: { number: "1", unit: "e+" }
+  },
+  {
+    fixture: "1e-",
+    expected: { number: "1", unit: "e-" }
+  },
+  {
+    fixture: "1e+1",
+    expected: { number: "1e+1", unit: "" }
+  },
+  {
+    fixture: "1e++1",
+    expected: { number: "1", unit: "e++1" }
+  },
+  {
+    fixture: "1e--1",
+    expected: { number: "1", unit: "e--1" }
+  },
+  {
+    fixture: "+10",
+    expected: { number: "+10", unit: "" }
+  },
+  {
+    fixture: "-10",
+    expected: { number: "-10", unit: "" }
+  },
+  {
+    fixture: ".2px",
+    expected: { number: ".2", unit: "px" }
+  },
+  {
+    fixture: "-.2px",
+    expected: { number: "-.2", unit: "px" }
+  },
+  {
+    fixture: "+.2px",
+    expected: { number: "+.2", unit: "px" }
+  },
+  {
+    fixture: ".a",
+    expected: false
+  },
+  {
+    fixture: ".",
+    expected: false
+  },
+  {
+    fixture: "+",
+    expected: false
+  },
+  {
+    fixture: "-",
+    expected: false
+  },
+  {
+    fixture: "-a",
+    expected: false
+  },
+  {
+    fixture: "+a",
+    expected: false
+  },
+  {
+    fixture: "+.a",
+    expected: false
+  },
+  {
+    fixture: "-.a",
+    expected: false
+  },
+  {
+    fixture: "",
+    expected: false
   }
 ];