In order to understand how each of the classes of extensions work, one should start by looking at the WiX source code. All extensions have the following things in common:
Before investing in an extension, one should evaluate whether an external tool and the ?include? syntax (from the preprocessor) will provide the needed flexibility for your technical needs.
Multiple extensions and extension types are supported, but there is no guarantee of the order in which a particular class of extensions will be processed. As a result, there must not be any sequencing dependencies between extensions within the same extension class.
Extension developers might also implement a RequiredVersion attribute on the Wix element. This allows setup developers using your extension to require a specific version of the extension in case a new feature is introduced or a breaking change is made. You can add an attribute to the Wix element in an extension as shown in the following example.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xse="http://schemas.microsoft.com/wix/2005/XmlSchemaExtension"> <xs:attribute name="RequiredVersion" type="xs:string"> <xs:annotation> <xs:documentation> The version of this extension required to compile the defining source. </xs:documentation> <xs:appinfo> <xse:parent namespace="http://schemas.microsoft.com/wix/2006/wi" ref="Wix" /> </xs:appinfo> </xs:annotation> </xs:attribute> </xs:schema>