Content types in SharePoint

Content types in SharePoint can be extended by creating a new feature which deploys an element file with the following content:

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
    <ContentType ID="GUID"
        Name="Text"
        Group="Text"
        Version="0">
        <FieldRefs>
            <FieldRef ID="GUID" Name="Text"/>
        </FieldRefs>
    </ContentType>
</Elements>

The content type Id includes the GUID of the Parent content type. The base content type (System) has an Id of 0x. The Id is built up as follows:

Option 1

[ParentGUID][01]
[ParentGUID][02]
[ParentGUID][03]
…

Option 2

[ParentGUID]00[GUID]

Out of the box examples for the first format are as below:

Examples of the second format are:

Which format should be used?

SharePoint uses the long GUIDs when you create a new content type however it does mean that you might end up with very long set of characters making it almost impossible to manage. Personally I prefer the short version however I also like to follow the standard set by SharePoint. The only real limitation of the short version of the Content type ID is that you can only inherit 254 times from a base content type.

The main thing to consider there is that when the next release of SharePoint comes out will there be any duplicate Id in use in your solution. Therefore to avoid duplicate IDs use a long GUID when you create base content type which extends an out of the box content type (such as Item or Document). Then when you extend your base content type you can use 01, 02, 03 etc.