[Qgis-developer] 2 additional options in the Spatial Query plugin need to be explained

[Larissa Junek]

Hello,

I am currently working on the QGIS user manual 2.8 and deal with two
options in the Spatial Query plugin we didn't explain so far:
- invalid source (source with geometry errors?)
- invalid reference

While 'Result feature IDs' when having run the plugin is easy to
understand we didn't manage to explain what the function of the other
two options is.

Can somebody help me?

Cheers, 
Larissa