I tried to create a "jboss-web.xml" file based on the "jboss-web_7_1.xsd"

As this is not uploaded to the web up to now, I created it with a schema location pointing to my local JBoss 7.2.0Alpha1 snapshot:

<?xml version="1.0" encoding="UTF-8"?>
<jboss-web xmlns="http://www.jboss.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.jboss.com/xml/ns/javaee file:///C:/Temp/jboss-as-7.2.0.Alpha1-SNAPSHOT/docs/schema/jboss-web_7_0.xsd"
version="7.0">
...

</jboss-web>

Eclipse shows validation errors in the XSD file.

The first on is:
sch-props-correct.2: A schema cannot contain two global components with the same name; this schema contains two
occurences of 'http://java.sun.com/xml/ns/javaee,descriptionGroup'
(occurs in javaee_6.xsd, line 88)
And a lot more of those.

The file was created as part of https://issues.jboss.org/browse/AS7-1262 - and the one who created it found the same validation error.

It seems the fix is quite simple:
"jboss-web_7_0.xsd" contains this import:

<xsd:import namespace="http://java.sun.com/xml/ns/javaee" schemaLocation="web-app_3_0.xsd"/>

Change it to:
<xsd:import namespace="http://java.sun.com/xml/ns/javaee" schemaLocation="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"/>

The reason seems to be: "jboss-web_7_0.xsd" imports "jboss-common_6-0.xsd", and this one imports "javaee_6.xsd" with a full schema location.
The "web-app_3_0.xsd" in "jboss-web_7_0.xsd" has a local schema location, thus the "javaee_6.xsd" import in "web-app_3_0.xsd" points also to local.
And this seems to cause a duplicate import of the file.

(might also be an Eclipse valiation bug)