In the MSDN documentation, I see fragments that look like XSD for the PROPDESC files for things like propertyDescriptionList attributes. Is the whole schema definition somewhere so I can validate my .propdesc file?
Here's the sample propdesc file from the Windows 7 SDK sample, for what that's worth. The sample defines a custom file type of .recipe.
<?xml version="1.0" encoding="utf-8"?>
<!--
This propdesc file contains the descriptions of Recipe Sample custom properties.
To register/unregister, use the PropertySchema SDK sample, or http://www.codeplex.com/prop.
-->
<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://schemas.microsoft.com/windows/2006/propertydescription"
schemaVersion="1.0">
<propertyDescriptionList publisher="Microsoft" product="SampleRecipe">
<propertyDescription name="Microsoft.SampleRecipe.Difficulty" formatID="{1794C9FE-74A9-497f-9C69-B31F03CE7EF9}" propID="100">
<description>This property indicates the preparation difficulty of a recipe.</description>
<searchInfo inInvertedIndex="true" isColumn="true" columnIndexType="OnDisk" mnemonics="RecipeDifficulty"/>
<typeInfo type="String" multipleValues="false" isViewable="true" isQueryable="true"/>
<labelInfo label="Recipe difficulty" invitationText="Specify recipe difficulty" />
<displayInfo displayType="Enumerated" >
<editControl control="DropList"/>
<enumeratedList>
<enum value="Easy" text="Easy" />
<enum value="Medium" text="Medium" />
<enum value="Hard" text="Hard" />
</enumeratedList>
</displayInfo>
</propertyDescription>
</propertyDescriptionList>
</schema>
Update: there's a note at MSDN requiring an xmlns reference to http://schemas.microsoft.com/windows/2006/propertydescription but that's just a placeholder URL as far as I can tell.
I finally just created an empty xsd file in Visual Studio and started plugging in the various pieces. I got it working well enough, with the exception of missing simple types for upcase-uuid and canonical-name, which I don't see in the docs. Anyway, I was able to use the XML Plugin in Notepad++ to validate my .propdesc file against this schema, and it found an error for me, so I thought I'd share.
<?xml version="1.0" encoding="utf-8"?>
<xs:schema targetNamespace="http://schemas.microsoft.com/windows/2006/propertydescription"
elementFormDefault="qualified"
xmlns="http://schemas.microsoft.com/windows/2006/propertydescription"
xmlns:mstns="http://tempuri.org/XMLSchema.xsd"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
>
<xs:element name="schema">
<xs:complexType>
<xs:sequence>
<xs:element ref="propertyDescriptionList" minOccurs="1" maxOccurs="1"/>
</xs:sequence>
<xs:attribute name="schemaVersion" type="xs:string"/>
</xs:complexType>
</xs:element>
<!-- propertyDescriptionList -->
<xs:element name="propertyDescriptionList">
<xs:complexType>
<xs:sequence>
<xs:element ref="propertyDescription" minOccurs="1" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="publisher" type="xs:string"/>
<xs:attribute name="product" type="xs:string"/>
</xs:complexType>
</xs:element>
<!-- propertyDescription -->
<xs:element name="propertyDescription">
<xs:complexType>
<xs:all>
<xs:element name="description" type="xs:string" minOccurs="0" maxOccurs="1"/>
<xs:element ref="searchInfo" minOccurs="1" maxOccurs="1"/>
<xs:element ref="labelInfo" minOccurs="0" maxOccurs="1"/>
<xs:element ref="typeInfo" minOccurs="0" maxOccurs="1"/>
<xs:element ref="displayInfo" minOccurs="0" maxOccurs="1"/>
</xs:all>
<!--<xs:attribute name="formatID" type="upcase-uuid" use="required"/>-->
<xs:attribute name="formatID" type="xs:string" use="required"/>
<xs:attribute name="propID" type="xs:nonNegativeInteger" use="required"/>
<!--<xs:attribute name="name" type="canonical-name" use="required"/>-->
<xs:attribute name="name" type="xs:string" use="required"/>
</xs:complexType>
</xs:element>
<!-- displayInfo -->
<xs:element name="displayInfo">
<xs:complexType>
<xs:all>
<xs:element name="stringFormat" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="formatAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="General"/>
<xs:enumeration value="FileName"/>
<xs:enumeration value="FilePath"/>
<xs:enumeration value="Hyperlink"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="booleanFormat" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="formatAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="YesNo"/>
<xs:enumeration value="OnOff"/>
<xs:enumeration value="TrueFalse"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="numberFormat" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="formatAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="General"/>
<xs:enumeration value="Percentage"/>
<xs:enumeration value="ByteSize"/>
<xs:enumeration value="KBSize"/>
<xs:enumeration value="SampleSize"/>
<xs:enumeration value="Bitrate"/>
<xs:enumeration value="SampleRate"/>
<xs:enumeration value="FrameRate"/>
<xs:enumeration value="Pixels"/>
<xs:enumeration value="DPI"/>
<xs:enumeration value="Duration"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="formatDurationAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="hh:mm"/>
<xs:enumeration value="hh:mm:ss"/>
<xs:enumeration value="hh:mm:ss.fff"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="dateTimeFormat" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="formatAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="General"/>
<xs:enumeration value="Month"/>
<xs:enumeration value="YearMonth"/>
<xs:enumeration value="Year"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="formatTimeAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="ShortTime"/>
<xs:enumeration value="LongTime"/>
<xs:enumeration value="HideTime"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="formatDateAs">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="ShortDate"/>
<xs:enumeration value="LongDate"/>
<xs:enumeration value="HideDate"/>
<xs:enumeration value="RelativeShortDate"/>
<xs:enumeration value="RelativeLongDate"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="enumeratedList" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:sequence>
<xs:element name="enum" minOccurs="0" maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="value" type="xs:string" use="required"/>
<xs:attribute name="text" type="xs:string" use="required"/>
</xs:complexType>
</xs:element>
<xs:element name="enumRange" minOccurs="0" maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="minValue" type="xs:string" use="required"/>
<xs:attribute name="setValue" type="xs:string"/>
<xs:attribute name="text" type="xs:string"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="defaultText" type="xs:string"/>
<xs:attribute name="useValueForDefault" type="xs:boolean"/>
</xs:complexType>
</xs:element>
<xs:element name="drawControl" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="control">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Default"/>
<xs:enumeration value="MultiLineText"/>
<xs:enumeration value="MultiValueText"/>
<xs:enumeration value="PercentBar"/>
<xs:enumeration value="ProgressBar"/>
<xs:enumeration value="Rating"/>
<xs:enumeration value="StaticText"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="editControl" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="control">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Default"/>
<xs:enumeration value="Calendar"/>
<xs:enumeration value="CheckboxDropList"/>
<xs:enumeration value="DropList"/>
<xs:enumeration value="MultiLineText"/>
<xs:enumeration value="MultiValueText"/>
<xs:enumeration value="Rating"/>
<xs:enumeration value="Text"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="filterControl" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="control">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Default"/>
<xs:enumeration value="Calendar"/>
<xs:enumeration value="Rating"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="queryControl" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="control">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Default"/>
<xs:enumeration value="Boolean"/>
<xs:enumeration value="Calendar"/>
<xs:enumeration value="CheckboxDropList"/>
<xs:enumeration value="DropList"/>
<xs:enumeration value="MultiValueText"/>
<xs:enumeration value="NumericText"/>
<xs:enumeration value="Rating"/>
<xs:enumeration value="Text"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:all>
<xs:attribute name="defaultColumnWidth" type="xs:nonNegativeInteger" default="20"/>
<xs:attribute name="displayType">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="String"/>
<xs:enumeration value="Number"/>
<xs:enumeration value="Boolean"/>
<xs:enumeration value="DateTime"/>
<xs:enumeration value="Enumerated"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="alignment" default="Left">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Left"/>
<xs:enumeration value="Center"/>
<xs:enumeration value="Right"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="relativeDescriptionType">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="General"/>
<xs:enumeration value="Date"/>
<xs:enumeration value="Size"/>
<xs:enumeration value="Count"/>
<xs:enumeration value="Revision"/>
<xs:enumeration value="Length"/>
<xs:enumeration value="Duration"/>
<xs:enumeration value="Speed"/>
<xs:enumeration value="Rate"/>
<xs:enumeration value="Rating"/>
<xs:enumeration value="Priority"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="defaultSortDirection" default="Ascending">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Ascending"/>
<xs:enumeration value="Descending"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<!-- searchInfo for Windows 7-->
<xs:element name="searchInfo">
<xs:complexType>
<xs:attribute name="inInvertedIndex" type="xs:boolean" default="false"/>
<xs:attribute name="isColumn" type="xs:boolean" default="false"/>
<xs:attribute name="isColumnSparse" type="xs:boolean" default="true">
<xs:annotation>
<xs:documentation>
isColumnSparse: Default is true. If the property is multi-valued, this is always true.
</xs:documentation>
</xs:annotation>
</xs:attribute>
<xs:attribute name="columnIndexType" default="OnDemand">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="NotIndexed"/>
<xs:enumeration value="OnDisk"/>
<xs:enumeration value="OnDiskAll"/>
<xs:enumeration value="OnDiskVector"/>
<xs:enumeration value="OnDemand"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="maxSize" type="xs:nonNegativeInteger" default="512"/>
<xs:attribute name="mnemonics" type="xs:string"/>
</xs:complexType>
</xs:element>
<!-- labelInfo -->
<xs:element name="labelInfo">
<xs:complexType>
<xs:attribute name="label" type="xs:string"/>
<xs:attribute name="sortDescription">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="General"/>
<xs:enumeration value="AToZ"/>
<xs:enumeration value="LowestHighest"/>
<xs:enumeration value="OldestNewest"/>
<xs:enumeration value="SmallestLargest"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="invitationText" type="xs:string"/>
<xs:attribute name="hideLabel" type="xs:boolean" default="false"/>
</xs:complexType>
</xs:element>
<!-- typeInfo for Windows 7-->
<xs:element name="typeInfo">
<xs:complexType>
<xs:attribute name="type" default="Any">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Any"/>
<xs:enumeration value="Null"/>
<xs:enumeration value="String"/>
<xs:enumeration value="Boolean"/>
<xs:enumeration value="Byte"/>
<xs:enumeration value="Buffer"/>
<xs:enumeration value="Int16"/>
<xs:enumeration value="UInt16"/>
<xs:enumeration value="Int32"/>
<xs:enumeration value="UInt32"/>
<xs:enumeration value="Int64"/>
<xs:enumeration value="UInt64"/>
<xs:enumeration value="Double"/>
<xs:enumeration value="DateTime"/>
<xs:enumeration value="Guid"/>
<xs:enumeration value="Blob"/>
<xs:enumeration value="Stream"/>
<xs:enumeration value="Clipboard"/>
<xs:enumeration value="Object"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="groupingRange">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Discrete"/>
<xs:enumeration value="Alphanumeric"/>
<xs:enumeration value="Size"/>
<xs:enumeration value="Date"/>
<xs:enumeration value="Dynamic"/>
<xs:enumeration value="Percent"/>
<xs:enumeration value="Enumerated"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="isInnate" type="xs:boolean" default="false"/>
<xs:attribute name="canBePurged" type="xs:boolean"/>
<xs:attribute name="multipleValues" type="xs:boolean" default="false"/>
<xs:attribute name="isGroup" type="xs:boolean" default="false"/>
<xs:attribute name="aggregationType">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Default"/>
<xs:enumeration value="First"/>
<xs:enumeration value="Sum"/>
<xs:enumeration value="Average"/>
<xs:enumeration value="DateRange"/>
<xs:enumeration value="Union"/>
<xs:enumeration value="Maximum"/>
<xs:enumeration value="Minimum"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="isTreeProperty" type="xs:boolean" default="false"/>
<xs:attribute name="isViewable" type="xs:boolean" default="false"/>
<xs:attribute name="isQueryable" type="xs:boolean" default="false"/>
<xs:attribute name="includeInFullTextQuery" type="xs:boolean" default="false"/>
<xs:attribute name="searchRawValue" type="xs:boolean" default="false"/>
<xs:attribute name="conditionType">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="None"/>
<xs:enumeration value="String"/>
<xs:enumeration value="Number"/>
<xs:enumeration value="DateTime"/>
<xs:enumeration value="Boolean"/>
<xs:enumeration value="Size"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="defaultOperation">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Equal"/>
<xs:enumeration value="NotEqual"/>
<xs:enumeration value="LessThan"/>
<xs:enumeration value="GreaterThan"/>
<xs:enumeration value="Contains"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>