<?xml version="1.0" encoding="UTF-8"?>
<!--
  Comprehensive XML Namespaces for HTML Versions 1-5
  Date: 2026-01-29

  HTML 1.0:
    Namespace URI: http://www.w3.org/TR/1992/WD-html-19921108/
    Example: <html xmlns="http://www.w3.org/TR/1992/WD-html-19921108/">...</html>

  HTML 2.0:
    Namespace URI: http://www.w3.org/TR/REC-html2/
    Example: <html xmlns="http://www.w3.org/TR/REC-html2/">...</html>

  HTML 3.2:
    Namespace URI: http://www.w3.org/TR/REC-html32/
    Example: <html xmlns="http://www.w3.org/TR/REC-html32/">...</html>

  HTML 4.01:
    Namespace URI: http://www.w3.org/TR/html4/
    Example: <html xmlns="http://www.w3.org/TR/html4/">...</html>

  HTML 5:
    Namespace URI: http://www.w3.org/1999/xhtml
    Example: <html xmlns="http://www.w3.org/1999/xhtml">...</html>
-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://www.example.com/custom-namespace"
           xmlns="http://www.example.com/custom-namespace"
           elementFormDefault="qualified">
  <!-- Custom simple types -->
  <xs:simpleType name="customString">
    <xs:restriction base="xs:string"/>
  </xs:simpleType>
  <xs:simpleType name="customBoolean">
    <xs:restriction base="xs:string">
      <xs:enumeration value="true"/>
      <xs:enumeration value="false"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="customID">
    <xs:restriction base="xs:string">
      <xs:pattern value="[A-Za-z_][A-Za-z0-9_\-\.]*"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="customURI">
    <xs:restriction base="xs:string"/>
  </xs:simpleType>
  <!-- Global attributes for all elements -->
  <xs:attributeGroup name="globalAttrs">
    <xs:attribute name="id" type="customID" use="optional"/>
    <xs:attribute name="class" type="customString" use="optional"/>
    <xs:attribute name="style" type="customString" use="optional"/>
    <xs:attribute name="lang" type="customString" use="optional"/>
    <xs:attribute name="title" type="customString" use="optional"/>
    <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:attributeGroup>
  <!-- Example: <a> element with custom types -->
  <xs:element name="a">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="customString">
          <xs:attributeGroup ref="globalAttrs"/>
          <xs:attribute name="href" type="customURI" use="optional"/>
          <xs:attribute name="target" type="customString" use="optional"/>
          <xs:attribute name="rel" type="customString" use="optional"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
  <!-- Example: <img> element with custom types -->
  <xs:element name="img">
    <xs:complexType>
      <xs:attributeGroup ref="globalAttrs"/>
      <xs:attribute name="src" type="customURI" use="required"/>
      <xs:attribute name="alt" type="customString" use="required"/>
      <xs:attribute name="width" type="customString" use="optional"/>
      <xs:attribute name="height" type="customString" use="optional"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <button> with restricted type attribute -->
  <xs:simpleType name="customButtonType">
    <xs:restriction base="customString">
      <xs:enumeration value="button"/>
      <xs:enumeration value="submit"/>
      <xs:enumeration value="reset"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:element name="button">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="customString">
          <xs:attributeGroup ref="globalAttrs"/>
          <xs:attribute name="type" type="customButtonType" use="optional" default="button"/>
          <xs:attribute name="disabled" type="customBoolean" use="optional"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
  <!-- Example: <ul> and <li> content model -->
  <xs:element name="ul">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="li" minOccurs="1" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attributeGroup ref="globalAttrs"/>
    </xs:complexType>
  </xs:element>
  <xs:element name="li">
    <xs:complexType mixed="true">
      <xs:attributeGroup ref="globalAttrs"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <input> with custom types -->
  <xs:simpleType name="customInputType">
    <xs:restriction base="customString">
      <xs:enumeration value="text"/>
      <xs:enumeration value="password"/>
      <xs:enumeration value="checkbox"/>
      <xs:enumeration value="radio"/>
      <xs:enumeration value="submit"/>
      <xs:enumeration value="reset"/>
      <xs:enumeration value="file"/>
      <xs:enumeration value="hidden"/>
      <xs:enumeration value="button"/>
      <xs:enumeration value="email"/>
      <xs:enumeration value="number"/>
      <xs:enumeration value="date"/>
      <xs:enumeration value="url"/>
      <xs:enumeration value="search"/>
      <xs:enumeration value="tel"/>
      <xs:enumeration value="color"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:element name="input">
    <xs:complexType>
      <xs:attributeGroup ref="globalAttrs"/>
      <xs:attribute name="type" type="customInputType" use="optional" default="text"/>
      <xs:attribute name="name" type="customString" use="optional"/>
      <xs:attribute name="value" type="customString" use="optional"/>
      <xs:attribute name="placeholder" type="customString" use="optional"/>
      <xs:attribute name="checked" type="customBoolean" use="optional"/>
      <xs:attribute name="disabled" type="customBoolean" use="optional"/>
      <xs:attribute name="readonly" type="customBoolean" use="optional"/>
      <xs:attribute name="required" type="customBoolean" use="optional"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <div> as a generic container with extensibility -->
  <xs:element name="div">
    <xs:complexType mixed="true">
      <xs:sequence minOccurs="0" maxOccurs="unbounded">
        <xs:any namespace="##any" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attributeGroup ref="globalAttrs"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <span> as a generic inline container -->
  <xs:element name="span">
    <xs:complexType mixed="true">
      <xs:sequence minOccurs="0" maxOccurs="unbounded">
        <xs:any namespace="##any" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attributeGroup ref="globalAttrs"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <h1> to <h6> headings with global attributes -->
  <xs:complexType name="customHeadingType">
    <xs:simpleContent>
      <xs:extension base="customString">
        <xs:attributeGroup ref="globalAttrs"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
  <xs:element name="h1" type="customHeadingType"/>
  <xs:element name="h2" type="customHeadingType"/>
  <xs:element name="h3" type="customHeadingType"/>
  <xs:element name="h4" type="customHeadingType"/>
  <xs:element name="h5" type="customHeadingType"/>
  <xs:element name="h6" type="customHeadingType"/>
  <!-- Example: <meta> with custom types -->
  <xs:element name="meta">
    <xs:complexType>
      <xs:attributeGroup ref="globalAttrs"/>
      <xs:attribute name="name" type="customString" use="optional"/>
      <xs:attribute name="content" type="customString" use="optional"/>
      <xs:attribute name="charset" type="customString" use="optional"/>
      <xs:attribute name="http-equiv" type="customString" use="optional"/>
    </xs:complexType>
  </xs:element>
  <!-- Example: <table> with content model and extensibility -->
  <xs:element name="table">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="caption" minOccurs="0" maxOccurs="1"/>
        <xs:element name="thead" minOccurs="0" maxOccurs="1"/>
        <xs:element name="tbody" minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="tfoot" minOccurs="0" maxOccurs="1"/>
      </xs:sequence>
      <xs:attributeGroup ref="globalAttrs"/>
    </xs:complexType>
  </xs:element>
  <!-- ...existing code for other elements, all using only custom types... -->
</xs:schema>
