The ValueDefinition class defines a type of value collection and associates a keyword with it.

The definition specifies the means of creating the collection rather than the value set itself; the specification may for example be an SQL statement, a file name, an array variable, an explicit list, or some other list source.

A userclass ValueDefinitionProxy, provided in the Core application, has a ListTextValues method that evaluates a value definition specification and return a choice list of the values.

This method is used by the Workbench tagged values editor (Extension Properties dialog) to provide lookup lists of tag values for tag types such as "category," "subtype," and "rw."

The TagDefinition attribute TagValues (see TagValues Attribute) contains an array of ValueDefinition, used to define the set of values that a given type of tagged value may use for its allowed or example values. The value definition keywords used by the tag definitions defined in appedtags.xml are themselves defined in the file appedvalues.xml. Developers who customize the usertags.xml file can use uservalues.xml to define their own keywords in the same way.