Working on the WS-Mex primer, I noticed it's not possible to say the following with the current syntax:
"Get all the metadata supported by an endpoint, return it inlined"

This is because, in order to say "Get all the metadata" you need to omit the dialect element. 
However, the Dialect elemet is required in order to specify the Content attribute (which indicates that the returned metadata should be inlined).

There are a number of ways we could fix this:

Proposal 1
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Move the Content attribute to the GetMetadata
This places the restriction that you can only specify one content type for all metadata.

Proposal 2
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Allow the Content attribute on GetMetadata only when no dialects are specified.  

Proposal 3
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Allow the Content attribute on GetMetadata.  
When Content Attributes also appear on the Dialect, they override (i.e. the one on the GetMetadata is the default).