[css-text-3] Provide an overview of the line-breaking properties in the section intro. Clean up some text about interactions. w3c#2559

Author: fantasai

css-text-3/Overview.bs

@@ -861,7 +861,8 @@ Characters and Letters</h3>
 
   <p>When inline-level content is laid out into lines, it is broken across line boxes.
     Such a break is called a <dfn>line break</dfn>.
-    When a line is broken due to explicit line-breaking controls,
+    When a line is broken due to explicit line-breaking controls
+    (such as a <a>preserved</a> newline character),
     or due to the start or end of a block,
     it is a <dfn>forced line break</dfn>.
     When a line is broken due to content <dfn lt="wrapping|wrap">wrapping</dfn>
@@ -899,17 +900,37 @@ Characters and Letters</h3>
     Additionally the level of strictness in these restrictions
     varies with the typesetting style.
 
-  <p>CSS does not fully define where <a>soft wrap opportunities</a> occur;
-    however some controls are provided to distinguish common variations.
+  <p>While CSS does not fully define where <a>soft wrap opportunities</a> occur,
+    some controls are provided to distinguish common variations:
+
+  <ul>
+    <li>
+      The 'line-break' property allows choosing various levels of “strictness”
+      for line breaking restrictions.
+    <li>
+      The 'word-break' property controls what types of letters
+      are glommed together to form unbreakable “words”,
+      causing CJK characters to behave like non-CJK text or vice versa.
+    <li>
+      The 'hyphens' property controls whether automatic hyphenation
+      is allowed to break words in scripts that hyphenate.
+    <li>
+      The 'overflow-wrap' property allows the UA to take a break anywhere
+      in otherwise-unbreakable strings that would otherwise overflow.
+  </ul>
 
   <div class="note">
     <p>Note: Further information on line breaking conventions can be found in
       [[JLREQ]] and [[JIS4051]] for Japanese,
-      [[ZHMARK]] for Chinese, and
+      [[CLREQ]] and [[ZHMARK]] for Chinese, and
       in [[!UAX14]] for all scripts in Unicode.
+      See also the
+      <a href="https://www.w3.org/International/">Internationalization Working Group</a>’s
+      <a href="https://www.w3.org/TR/typography/#blocks_paragraphs">Typography Index</a> [[TYPOGRAPHY]]
+      which includes more information on additional languages.
 
-    <p class="feedback issue">Any guidance for appropriate references here would be
-      much appreciated.
+    <p class="feedback issue">Any guidance for additional appropriate references
+      would be much appreciated.
   </div>
 
 <h3 id="line-break-details">
@@ -919,20 +940,24 @@ Line Breaking Details</h3>
   <ul>
     <li>Regardless of the 'white-space' value,
       lines always break at each <a>preserved</a> forced break character:
+      thus
       for all values, line-breaking behavior defined for
       the BK, CR, LF, CM, NL, and SG line breaking classes in [[!UAX14]]
       must be honored.
-    <li>When 'white-space' allows wrapping,
-      line breaking behavior defined for the WJ, ZW, and GL line-breaking classes in [[!UAX14]]
+    <li>Except where explicitly defined otherwise
+      (e.g. for ''line-break: anywhere'' or ''overflow-wrap: anywhere'')
+      line breaking behavior defined for
+      the WJ, ZW, and GL line-breaking classes in [[!UAX14]]
       must be honored.
     <li>UAs that allow wrapping at punctuation other than spaces should prioritize breakpoints.
-      For example, if breaks after slashes are given a lower priority than spaces,
-      the sequence "check /etc" will never break between the "/" and the "e".
+      (For example, if breaks after slashes are given a lower priority than spaces,
+      the sequence "check /etc" will never break between the "/" and the "e".)
       As long as care is taken to avoid such awkward breaks, allowing breaks at
       appropriate punctuation other than spaces is recommended, as it results
       in more even-looking margins, particularly in narrow measures.
       The UA may use the width of the containing block, the text's language,
-      and other factors in assigning priorities.
+      and other factors in assigning priorities:
+      CSS does not define prioritization of line breaking opportunities.
     <li>Out-of-flow elements do not introduce a <a>forced line break</a>
       or <a>soft wrap opportunity</a> in the flow.
     <li>The line breaking behavior of a replaced element or other atomic inline
@@ -967,7 +992,8 @@ Line Breaking Details</h3>
 
     <p>This property specifies <a>soft wrap opportunities</a> between letters,
       i.e. where it is “normal” and permissible to break lines of text.
-      Specifically it controls whether a <a>soft wrap opportunity</a> exists
+      Specifically it controls whether a <a>soft wrap opportunity</a>
+      generally exists
       between adjacent <a>typographic letter units</a>
       (and/or non-<a>letter</a> <a>typographic character units</a>
       belonging to the
@@ -1014,18 +1040,23 @@ Line Breaking Details</h3>
 
       <dt><dfn>break-all</dfn></dt>
       <dd>Breaking is allowed within “words”:
-        in addition to ''word-break/normal'' <a>soft wrap opportunities</a>:
-        specifically, any <a>typographic character units</a> resolving to the
+        specifically,
+        in addition to <a>soft wrap opportunities</a> allowed for ''word-break/normal'',
+        any <a>typographic character units</a> resolving to the
         <code>NU</code> (“numeric”), <code>AL</code> (“alphabetic”), or <code>SA</code> (“Southeast Asian”)
         line breaking classes [[!UAX14]]
         are instead treated as <code>ID</code> (“ideographic characters”)
         for the purpose of line-breaking.
-        Hyphenation is not applied. This option is used mostly in a context where
-        the text consists predominantly of CJK characters with only short non-CJK excerpts,
-        and it is desired that the text be better distributed on each line.</dd>
-
-	Note: This value does not affect whether there are <a>soft wrap opportunities</a> around punctuation characters.
-	To allow breaks anywhere, see ''line-break: anywhere''.
+        Hyphenation is not applied.
+        This option is used mostly in a context where
+        the text consists predominantly of CJK characters
+        with only short non-CJK excerpts,
+        and it is desired that the text be better distributed on each line.
+
+        Note: This value does not affect
+        whether there are <a>soft wrap opportunities</a>
+        around punctuation characters.
+        To allow breaks anywhere, see ''line-break: anywhere''.
 
       <dt><dfn>keep-all</dfn></dt>
       <dd>Breaking is forbidden within “words”: