diff --git a/README.md b/README.md
index e2f0d5925..72cc391db 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,12 @@ DocBook on Linux or Windows, or what conventions you
 should follow when writing phpdoc files, please refer
 to the PHP Documentation HOWTO.
 
+The PHP Documentation uses the [DocBook 5.2](https://tdg.docbook.org/tdg/5.2/) XML schema. \
+However, there is one small change between the official Docbook 5.2 schema and the schema used by the PHP documentation:
+the `<classsynopsis>` tag allows "One or more Oriented Object Programming inlines",
+like the [DocBook 5.1](https://tdg.docbook.org/tdg/5.1/classsynopsis) schema does,
+instead of "One Oriented Object Programming inlines".
+
 You can read the HOWTO online at: http://doc.php.net/tutorial/
 
 If you are already working with the phpdoc module,
diff --git a/docbook/docbook-v5.2-os/rng/docbook.rng b/docbook/docbook-v5.2-os/rng/docbook.rng
index 61606a5dd..7490ce0b1 100755
--- a/docbook/docbook-v5.2-os/rng/docbook.rng
+++ b/docbook/docbook-v5.2-os/rng/docbook.rng
@@ -16249,7 +16249,9 @@ where the nonterminal
         <zeroOrMore>
           <ref name="db.templatename"/>
         </zeroOrMore>
-        <ref name="db.oo.inlines"/>
+        <oneOrMore>
+          <ref name="db.oo.inlines"/>
+        </oneOrMore>
         <zeroOrMore>
           <choice>
             <ref name="db.template"/>
diff --git a/docbook/docbook-v5.2-os/rng/docbookxi.rng b/docbook/docbook-v5.2-os/rng/docbookxi.rng
index c6b499eca..b22cc4e53 100755
--- a/docbook/docbook-v5.2-os/rng/docbookxi.rng
+++ b/docbook/docbook-v5.2-os/rng/docbookxi.rng
@@ -16394,7 +16394,9 @@ where the nonterminal
         <zeroOrMore>
           <ref name="db.templatename"/>
         </zeroOrMore>
-        <ref name="db.oo.inlines"/>
+        <oneOrMore>
+          <ref name="db.oo.inlines"/>
+        </oneOrMore>
         <zeroOrMore>
           <choice>
             <ref name="db.template"/>