Is this a bug in xmllint or xmlstarlet pattern matching? - regex

Question

Here is my product.xml file contents:
<ProductCode>ABC</ProductCode>
And here is the corresponding validating schema, product.xsd file contents:
<?xml version="1.0" encoding="utf-8"?>
<xsd:schema
version="1.0"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="ProductCode">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:minLength value="1"/>
<xsd:maxLength value="15"/>
<xsd:pattern value="[\P{Ll}]*"></xsd:pattern>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
</xsd:schema>
I open a command line shell, and used xmlstarlet to validate the xml:
xmlstarlet val -e --xsd product.xsd product.xml
product.xml:1.31: Element 'ProductCode': [facet 'pattern'] The value 'ABC' is not accepted by the pattern '[\P{Ll}]*'.
product.xml:1.31: Element 'ProductCode': 'ABC' is not a valid value of the local atomic type.
product.xml - invalid
Then, i tried to use xmllint to validate the xml:
└xmllint -schema product.xsd product.xml
<?xml version="1.0"?>
<ProductCode>ABC</ProductCode>
Element 'ProductCode': [facet 'pattern'] The value 'ABC' is not accepted by the pattern '[\P{Ll}]*'.
Element 'ProductCode': 'ABC' is not a valid value of the local atomic type.
product.xml fails to validate
I spent a couple of hours tinkering with it and I found that I can make it work by removing the enclosing brackets:
<xsd:pattern value="\P{Ll}*"></xsd:pattern>
I can retain the enclosing brackets and make it work by using the /p inclusive pattern category and preceding it by a negation ^:
<xsd:pattern value="[^\p{Ll}]*"></xsd:pattern>
It seems, that there is a bug in the underlying implementation of xmllint and xmlstarlet and I need confirmation if indeed this is the case.
The versions I used are:
xmllint:
xmllint --version
xmllint: using libxml version 20904
compiled with: Threads Tree Output Push Reader Patterns Writer SAXv1 FTP HTTP DTDValid HTML Legacy C14N Catalog XPath XPointer XInclude Iconv ISO8859X Unicode Regexps Automata Expr Schemas Schematron Modules Debug Zlib Lzma
xmlstarlet:
xmlstarlet --version
1.6.1
compiled against libxml2 2.9.1, linked with 20904
compiled against libxslt 1.1.28, linked with 10129
Additional Info
Using python as coded in the snippets in python XML schema validation snippets, i found that product.xsd does not validate product.xml also. It's hard to believe that python also has this bug. So therefore, I am now seeking some kind of explanation why the pattern expression in product.xsd is not working.
The question is: why is the enclosing bracket not able to work with the exclusive /P{Ll} ?
More Additional Info
On the other hand, using the scala snippet here,it is able to validate product.xml via product.xsd. So now, we can confirm that the pattern syntax in product.xsd is correct. Yet, xmllint, xmlstarlet and python could not validate it. What is going on here?