Add support for Schematron XML validation files (.sch)

Update languages.yml and add three public domain sample documents.

samples/XML/namespace-strict.sch

@@ -0,0 +1,84 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<schema xmlns="http://purl.oclc.org/dsdl/schematron"
+   queryBinding="xslt2"
+   xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+  <!-- XSLT 2.0 Schematron by Wendell Piez (Mulberry Technologies, Inc.),
+       August 2011 -->
+  
+  <!-- This Schematron is released into the public domain.     
+       Please credit your sources. -->
+  
+  
+  <!-- Requires Schematron that allows embedded XSLT 2.0 with support for
+       the namespace:: axis. Tested with Saxon 9.3.0.5. -->
+  
+  <ns prefix="m" uri="http://www.mulberrytech.com/xslt/util"/>
+  
+  <xsl:variable name="ns-set" xmlns:m="http://www.mulberrytech.com/xslt/util">
+    <!-- include elements to declare expected namespace prefixes
+         with their bindings, like so:
+
+         (prefix 'mml')
+         <m:ns prefix="mml"   uri="http://www.w3.org/1998/Math/MathML"/>
+         (default namespace, no prefix)
+         <m:ns prefix=""      uri="http://www.w3.org/1998/Math/MathML"/>
+         -->
+         
+    <m:ns prefix="mml"   uri="http://www.w3.org/1998/Math/MathML"/>
+    <m:ns prefix="xlink" uri="http://www.w3.org/1999/xlink"/>>
+    <m:ns prefix="oasis" uri="http://docs.oasis-open.org/ns/oasis-exchange/table"/>
+
+    <!-- 'xml' prefix is always in scope with this binding -->
+    <m:ns prefix="xml"   uri="http://www.w3.org/XML/1998/namespace"/>
+  </xsl:variable>
+  
+  <pattern>
+    <!-- checking the document element against the spec given in ns-set -->
+    <rule context="/*">
+      <let name="new-prefixes" value="in-scope-prefixes(.)[not(. = $ns-set/m:ns/@prefix)]"/>
+      <let name="new-namespaces" value="(for $p in (in-scope-prefixes(.)) return namespace-uri-for-prefix($p,.))
+        [not(. = $ns-set/m:ns/@uri)]"/>
+      <report test="exists($new-prefixes)">
+        Unrecognized namespace prefix<xsl:value-of select="('es')[count($new-prefixes) gt 1]"/>: 
+        <value-of select="string-join(
+          (for $p in $new-prefixes return m:label($p)),
+          ', ')"/>
+      </report>
+      <report test="exists($new-namespaces)">
+        Unrecognized namespace URI<xsl:value-of select="('s')[count($new-namespaces) gt 1]"/>: 
+        <value-of select="string-join(($new-namespaces),', ')"/>
+      </report>
+      
+      <let name="misassigned-prefixes" value="in-scope-prefixes(.)[not(.=$new-prefixes)]
+        [for $p in (.) return 
+          namespace-uri-for-prefix($p,current()) ne $ns-set/m:ns[@prefix=$p]/@uri]"/>
+      <report test="exists($misassigned-prefixes)">
+        Prefix<xsl:value-of select="('es')[count($misassigned-prefixes) gt 1]"/> 
+        assigned incorrectly: <value-of select="string-join(
+          (for $p in $misassigned-prefixes return
+          concat(m:label($p), ' (should be ''',$ns-set/m:ns[@prefix=$p]/@uri,''')')),
+          '; ')"/>
+      </report>
+    </rule>
+    
+    <!-- Elsewhere, all namespaces given must correspond with those
+      on the parent -->
+    <rule context="*">
+      <assert test="every $n in (namespace::*) satisfies
+        exists(../namespace::*[deep-equal(.,$n)])">
+        Namespace may not be declared here.
+      </assert>
+      <assert test="every $n in (../namespace::*) satisfies
+        exists(namespace::*[deep-equal(.,$n)])">
+        Namespace may not be undeclared here.
+      </assert>
+    </rule>
+  </pattern>
+  
+  <xsl:function name="m:label" as="xs:string">
+    <xsl:param name="label" as="xs:string"/>
+    <xsl:sequence select="if (string($label)) then concat('''',$label,'''') else '[unprefixed]'"/>
+  </xsl:function>
+  
+</schema>