part_of to VFBexp IDs should be allowed

[dosumis]

Naviely, it looks like this should be fixable by tweaking the regex as here:

78b7ae5#diff-7d40c8f169cf725408ddb5cbb4d7ae4baa6166c120e518d6a6a90eea4159abd2

But according to @Robbie1977 - this has been tried and fails.

[dosumis]

@Robbie1977 to document error messages here.