Add & nesting selector

Author: jacobcassidy

src/vscode-css/grammars/css.cson

@@ -1793,7 +1793,7 @@
             [-\\w*]+
             \\|
             (?!
-                [-\\[:.*\\#a-zA-Z_]    # Make sure there's a selector to match
+                [-\\[:.*&\\#a-zA-Z_]   # Make sure there's a selector to match
               | [^\\x00-\\x7F]
             )
           )
@@ -1811,6 +1811,10 @@
       {
         'include': '#tag-names'
       }
+      {
+        'match': '&'
+        'name': 'entity.name.tag.nesting.css'
+      }
       {
         'match': '\\*'
         'name': 'entity.name.tag.wildcard.css'
@@ -1836,7 +1840,7 @@
               # Consists of a hyphen only
               -                                      # Terminated by either:
               (?= $                                  # - End-of-line
-                | [\\s,.\\#)\\[:{>+~|]               # - Followed by another selector
+                | [\\s,.\\#)\\[:{>+~|&]              # - Followed by another selector
                 | /\\*                               # - Followed by a block comment
               )
               |
@@ -1846,7 +1850,7 @@
                 | \\\\(?:[0-9a-fA-F]{1,6}|.)         # - Escape sequence
               )*
               (?:                                    # Invalid punctuation
-                [!"'%&(*;<?@^`|\\]}]                 # - NOTE: We exempt `)` from the list of checked
+                [!"'%(*;<?@^`|\\]}]                  # - NOTE: We exempt `)` from the list of checked
                 |                                    #   symbols to avoid matching `:not(.invalid)`
                 / (?!\\*)                            # - Avoid invalidating the start of a comment
               )+
@@ -1877,7 +1881,7 @@
             )+
           )                                      # Followed by either:
           (?= $                                  # - End of the line
-            | [\\s,.\\#)\\[:{>+~|]               # - Another selector
+            | [\\s,.\\#)\\[:{>+~|&]              # - Another selector
             | /\\*                               # - A block comment
           )
         '''
@@ -1900,7 +1904,7 @@
             (?![0-9])
             (?:[-a-zA-Z0-9_]|[^\\x00-\\x7F]|\\\\(?:[0-9a-fA-F]{1,6}|.))+
           )
-          (?=$|[\\s,.\\#)\\[:{>+~|]|/\\*)
+          (?=$|[\\s,.\\#)\\[:{>+~|&]|/\\*)
         '''
         'name': 'entity.other.attribute-name.id.css'
       }
@@ -2103,7 +2107,7 @@
         | mrow|ms|mscarries|mscarry|msgroup|msline|mspace|msqrt|msrow|mstack|mstyle|msub|msubsup
         | msup|mtable|mtd|mtext|mtr|munder|munderover|semantics
       )
-      (?=[+~>\\s,.\\#|){:\\[]|/\\*|$)
+      (?=[+~>\\s,.\\#|&){:\\[]|/\\*|$)
     '''
     'name': 'entity.name.tag.css'
   'unicode-range':