Using author_sort, title_sort names
While creating a list of Calibre columns to show to users to allow customization, all the regular ones (authors, series, tags, ...) have names associated with them in field_metadata.py (Author(s), Series, Tags... But 'author_sort' doesn't.
I've noticed that 'Author Sort' doesn't appear on the list of columns you can display on the main GUI (e.g. in Preferences->Add your own columns).
"Author Sort" is used in the Edit Metadata screen for a book, so its obviously stored somewhere (though it appears to be hard coded in fetch_metadata). ('title_sort' and 'isbn' are the other fields on Edit Metadata that don't appear as column selections).
Clearly some fields are 'internal', but these 3 seemed inconsistent with the others that are displayed to the user at some point.
For my plugin, I can just ignore author_sort on the basis that it isn't a column they see in the main GUI and the user can simply create a custom column using that value if they really need it. (I can display it for them to use - but they would see 'author_sort' instead of 'Author Sort' unless I hard code the display, which I'll consider)