docs: Improve alt text on existing rewrite diagrams for accessibility

Replace vague or duplicated alt attributes with descriptive text that
conveys the content of each diagram to screen reader users:
- rewrite_process_uri.png: describes per-rule control flow
- rewrite_backreferences.png: describes \$1-\$9 and %1-%9 flow
- syntax_rewriterule.png: describes three-component syntax
- syntax_rewritecond.png: describes TestString and CondPattern components

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1935429 13f79535-47bb-0310-9956-ffa450edef68

diff --git a/docs/manual/rewrite/tech.xml b/docs/manual/rewrite/tech.xml
index 8e1eded63817242a9d013f7eb259ee1f21f6d8f7..8230bd5c6da3328bc8f650b29ca7d42c70c4c18f 100644 (file)
--- a/docs/manual/rewrite/tech.xml
+++ b/docs/manual/rewrite/tech.xml
@@ -233,7 +233,10 @@ RewriteRule "^/horses/ponies$" "/special-handler" [L]
       Figure 2 for more details.</p>
 <p class="figure">
       <img src="../images/rewrite_process_uri.png"
-          alt="Flow of RewriteRule and RewriteCond matching" /><br />
+          alt="Flowchart showing per-rule control flow: for each rule,
+          check pattern against URL, evaluate RewriteCond conditions,
+          apply substitution if both pass, then check flags to decide
+          whether to stop or continue to the next rule" /><br />
       <dfn>Figure 2:</dfn>The control flow through the rewriting ruleset
 </p>
       <p>First the URL is matched against the