Explain limitation of UnDefine syntax as already noted in Define.
Increase visibility of a warning, to be consistent with Define
PR 64909
@@ -4933,9 +4933,15 @@ certain events before failing a request</description>
<p>This directive can be used to toggle the use of <directive module="core"
type="section">IfDefine</directive> sections without needing to alter
<code>-D</code> arguments in any startup scripts.</p>
+
+ <p>Variable names may not contain colon ":" characters, to avoid clashes
+ with <directive module="mod_rewrite">RewriteMap</directive>'s syntax.</p>
+
+ <note><title>Virtual Host scope and pitfalls</title>
<p>While this directive is supported in virtual host context,
the changes it makes are visible to any later configuration
directives, beyond any enclosing virtual host.</p>
+ </note>
</usage>
<seealso><directive module="core">Define</directive></seealso>
<seealso><directive module="core">IfDefine</directive></seealso>
