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The editors

I tested each editor using the schema below, reading in the example XML document and trying to change it in invalid ways. I restricted myself to editors that are free for non-commercial use, which work under Linux and MacOS X and which don't require the installation of a log of new libraries.

XAmple

Home page: http://www.felixgolubov.com/XMLEditor
Needs only Java 1.5 or 1.6
Uses XML-handling Swing widgets designed by Golubov.
- No source code for the widgets, only a JAR file xmleditor.jar.
- Swing itself is part of the Java standard library.
The editor UI built around the widgets is called XAmple.
- We do get source code for XAmple.
Too-small font problem common to many Swing apps. Probably fixable.
Allows saving of malformed documents without asking for confirmation.
Understands xsi::noNamespaceSchemaLocation.
Generates an editing form from the schema.
Fast. Validation results appear without noticeable delay.

Rinzo

Home page: http://editorxml.sourceforge.net/
It's a plugin for Eclipse 3.3 or later.
SourceForge open source project.
No editing form. Documents are represented by syntax-colored text
in one pane together with a structure tree in another.
Doesn't understand xsi:: noNamespaceSchemaLocation.
- I had to use xsi::schemaLocation and give a bogus namespace URI
  along with the name of the schema file.
Slow. Noticeable delay between typing and the results of validation.
XML files must be part of an Eclipse project.
- If not then saves produce error pop-ups about invalid thread
  states.
Allows saving of malformed documents without asking for confirmation.
When inserting new elements it offers a menu of possibilities that
often includes invalid choices, allowing me to insert elements in the
wrong order. After insertion however the editor catches the error.

XMLmind XML Editor Personal Edition

Home page: http://www.xmlmind.com/xmleditor
Freeware Java 1.6, no source code.
- $330 Professional Edition comes with full source.
Schema glitch: It didn't accept the use of maxExclusive to restrict
the range of xs:unsignedInt.
- It claimed that maxExclusive and maxInclusive were both being used.
- I'll bet maxInclusive was used when deriving xs:unsignedInt
  from xs:integer.
- The two conditions should conflict only when used in the same
  restriction element.
- Fixed the problem by using xs:integer as the base and adding
  minInclusive="0".
Doesn't validate as you type. Validates upon load, save and upon
request.
Fast.
Offers the correct choices when inserting new elements.
Understands xsi:noNamespaceSchemaLocation.

The example XML document and schema

The schema file eeprom.xsd:

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="cmb1">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="boardSubtype"/>
        <xs:element ref="configSchema"/>
        <xs:element ref="fulcrumPort"/>
        <xs:element ref="mac"/>
        <xs:element ref="gatewayIp"/>
        <xs:element ref="netMask"/>
        <xs:element ref="endpoints"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name="endpoints">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="internal" minOccurs="0" maxOccurs="12"/>
        <xs:element ref="external" minOccurs="0" maxOccurs="26"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name="boardSubtype" type="xs:unsignedShort" />

  <xs:element name="configSchema">
    <xs:simpleType>
      <xs:restriction base="xs:unsignedInt">
        <!-- 14-bit unsigned int -->
        <xs:maxExclusive value="16384"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:element>

  <xs:element name="fulcrumPort"  type="xs:unsignedLong" />
  <xs:element name="mac"          type="macAddress" />
  <xs:element name="gatewayIp"    type="dottedIp" />
  <xs:element name="netMask"      type="dottedIp" />
  <xs:element name="type"         type="xs:unsignedByte" />
  <xs:element name="attr"         type="xs:unsignedByte" />

  <xs:element name="internal"     type="endpoint"/>
  <xs:element name="external"     type="endpoint"/>

  <xs:complexType name="endpoint">
    <xs:sequence>
      <xs:element ref="type"/>
      <xs:element ref="attr"/>
    </xs:sequence>
  </xs:complexType>

  <xs:simpleType name="macAddress">
    <!-- MAC addresses are to be only and exactly 6 bytes long. -->
    <xs:restriction base="xs:hexBinary">
      <xs:length value="6" />
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="dottedIp">
    <xs:restriction base="xs:string">
      <xs:pattern value="((1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])\.){3}(1?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])"/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>

The document eeprom_example.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!-- The root element is one of cmb1, cmb2, ftm or rtm. -->
<cmb1
  xsi:noNamespaceSchemaLocation="eeprom.xsd"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>
  <!-- Version info -->
  <boardSubtype>1</boardSubtype>
  <configSchema>1</configSchema>

  <!-- Routing and crossbar -->
  <fulcrumPort>0</fulcrumPort>
  <mac>ee0000aaaa00</mac>
  <gatewayIp>192.168.1.200</gatewayIp>
  <netMask>255.255.255.0</netMask>

  <endpoints>
    <!-- Internal endpoints first, then external. Slots are
         are assigned in the appropriate LUT in order of appearance.
    -->
    <internal>
      <type>1</type>
      <attr>15</attr>
    </internal>

    <internal>
      <type>3</type>
      <attr>42</attr>
    </internal>

    <internal>
      <type>0</type>
      <attr>7</attr>
    </internal>

    <external>
      <type>5</type>
      <attr>17</attr>
    </external>

    <external>
      <type>3</type>
      <attr>6</attr>
    </external>

  </endpoints>

</cmb1>