diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 59e76f5d..0c1c2a2d 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -6,6 +6,8 @@ AsciiDoc ChangeLog
 Version 8.5.4 (2010-08-15)
 --------------------------
 .Additions and changes
+- Relaxed anchor ID name syntax
+  (http://groups.google.com/group/asciidoc/browse_thread/thread/5f3e825c74ed30c).
 - Added document files: `doc/epub-notes.txt`,
   `doc/publishing-ebooks-with-asciidoc.txt`.
 - 'a2x': If all other resource locations are exhausted then recursively
diff --git a/asciidoc.conf b/asciidoc.conf
index acf940f9..f882c95a 100644
--- a/asciidoc.conf
+++ b/asciidoc.conf
@@ -194,11 +194,11 @@ CAUTION-style=template="admonitionparagraph",name="caution",caption="{caution-ca
 (?su)[\\]?(?P<name>footnote|footnoteref):(?P<target>\S*?)\[(?P<attrlist>.*?)\]=
 
 # Anchor: [[[id]]]. Bibliographic anchor.
-(?su)[\\]?\[\[\[(?P<attrlist>[\w][\w-]*?)\]\]\]=anchor3
+(?su)[\\]?\[\[\[(?P<attrlist>[\w_:][\w_:.-]*?)\]\]\]=anchor3
 # Anchor: [[id,xreflabel]]
-(?su)[\\]?\[\[(?P<attrlist>[\w"].*?)\]\]=anchor2
+(?su)[\\]?\[\[(?P<attrlist>[\w"_:].*?)\]\]=anchor2
 # Link: <<id,text>>
-(?su)[\\]?&lt;&lt;(?P<attrlist>[\w"].*?)&gt;&gt;=xref2
+(?su)[\\]?&lt;&lt;(?P<attrlist>[\w"_:].*?)&gt;&gt;=xref2
 
 ifdef::asciidoc7compatible[]
 # Index term: ++primary,secondary,tertiary++
diff --git a/doc/asciidoc.txt b/doc/asciidoc.txt
index 3abe2907..75262604 100644
--- a/doc/asciidoc.txt
+++ b/doc/asciidoc.txt
@@ -2091,10 +2091,11 @@ Used to specify hypertext link targets:
   [[<id>,<xreflabel>]]
   anchor:<id>[<xreflabel>]
 
-The `<id>` is a unique identifier that must begin with a letter. The
-optional `<xreflabel>` is the text to be displayed by captionless
-'xref' macros that refer to this anchor. The optional `<xreflabel>` is
-only really useful when generating DocBook output. Example anchor:
+The `<id>` is a unique string that conforms to the output markup's
+anchor syntax. The optional `<xreflabel>` is the text to be displayed
+by captionless 'xref' macros that refer to this anchor. The optional
+`<xreflabel>` is only really useful when generating DocBook output.
+Example anchor:
 
   [[X1]]
 
diff --git a/tests/data/testcases.txt b/tests/data/testcases.txt
index bd63a86a..ae180b48 100644
--- a/tests/data/testcases.txt
+++ b/tests/data/testcases.txt
@@ -155,6 +155,11 @@ An [[X3, anchor reftext]] inline anchor with reftext.
 
 Link to <<X3>> anchor.
 
+An example link to a bibliography entry <<Test::Unit>>.
+
+[horizontal]
+[[[Test::Unit]]]:: http://ruby-doc.org/stdlib/libdoc/test/unit/rdoc/classes/Test/Unit.html
+
 
 == Titles ==