[css-pseudo-4] Improve cross-linking to CSS Text 3.

Author: fantasai

css-pseudo-4/Overview.bs

@@ -279,7 +279,7 @@ First-Letter Text: ''::first-letter'' pseudo-element and its ''::prefix'' and ''
 
   The <dfn>::first-letter</dfn> [=pseudo-element=] represents
   the first Letter, Number, or Symbol
-  (Unicode category <code>L*</code>, <code>N*</code>, or <code>S*</code>) [=typographic character unit=]  [[!CSS-TEXT-3]]
+  (Unicode category <code>L*</code>, <code>N*</code>, or <code>S*</code>) [=typographic character unit=]
   on the <a>first formatted line</a> of its <a>originating element</a>
   (the <dfn>first letter</dfn>)
   as well as its associated punctuation.
@@ -296,7 +296,7 @@ First-Letter Text: ''::first-letter'' pseudo-element and its ''::prefix'' and ''
     <pre class="lang-css">h2 + p::first-letter { initial-letter: 2; }</pre>
   </div>
 
-  As explained in [[!CSS-TEXT-3]],
+  As explained in [[CSS-TEXT-3#characters]],
   a <a>typographic character unit</a> can include more than one Unicode codepoint.
   For example, combining characters must be kept with their base character.
   Also, languages may have additional rules
@@ -305,7 +305,8 @@ First-Letter Text: ''::first-letter'' pseudo-element and its ''::prefix'' and ''
   both letters should be considered within the ''::first-letter'' pseudo-element. [[UAX29]]
   When selecting the [=first letter=],
   the UA should tailor its definition of <a>typographic character unit</a>
-  to reflect the first-letter traditions of the ''::first-letter'' pseudo-element’s <em>containing block</em>’s content language.
+  to reflect the first-letter traditions of
+  the ''::first-letter'' pseudo-element’s <em>[=containing block=]</em>’s [=content language=].
 
   Note: Note that the [=first letter=] may in fact
   be a digit, e.g., the “6” in “67 million dollars is a lot of money.”
@@ -385,6 +386,11 @@ First-Letter Text: ''::first-letter'' pseudo-element and its ''::prefix'' and ''
   sub-[=pseudo-element=] of the ''::first-letter'' [=pseudo-element=]
   (''::first-letter::postfix'').
 
+  See [[css-text-3#characters]] and [[css-text-3#character-properties]]
+  for more information on [=typographic character units=]
+  and their Unicode properties.
+  [[!CSS-TEXT-3]]
+
 <h4 id="first-letter-application">
 Finding the First-Letter Text</h4>