BPEL code completion items show up in all XML files. BPELCompletionModelProvider
should prevent this.

The idea behind passing a CompletionContext to various CompletionModelProvider
implementation is that, they determine whether or not to return a list of
CompletionModels.

As an example, you can check the extension of the file

 if(!context.getPrimaryFile().getExt().equals("bpel"))
    return null;

Or, you may want to check something else and determine whether or not to return
a list of CompletionModels.