Is there any way to get the datatype of an input dataset in a tool xml? I can't seem to find it in any of the _MetadataElement_'s.
Would you please clarify your question?
If you trying to detect the datatype with the tool (or restrict which data will show up in a tool form's input menu by the datatype metadata attribute), there are many tools that do this. Find a tool that has the input filtered this way, examine the wrapper, then model your tool to be the same.
I think what you are looking for is discussed in depth here - http://planemo.readthedocs.org/en/latest/writing_how_do_i.html#check-input-type-in-command-blocks. Hope this helps.
Thanks! That's another resource I'll have to bookmark. I see there are some variables noted a readthdocs that aren't in the wiki. Isn't the wiki kept up to date by someone, or is this completely a community effort?
Please feel free to improve the wiki at any time!