[Shotwell] Restrictions on tag names (length, characters etc)

[Dougie Nisbet <dougie highmoor co uk>]

Is this a legal tagname?

    Sequoiadendron giganteum (Giant Sequoia, Wellingtonia, Giant Redwood)

It causes problems when I try to assign it, but it may be due to 
corruption in my database rather than something wrong with the tagname.

It creates corrupt mini-tags that are fragments of the full tagname.

I can get round it by deleting the tag and I suspect that it's the 
result of numerous exports/imports/re-installs/experimentation - but 
thought I'd check whether there are any restrictions on tagnames - e.g. 
illegal characters - that I should be aware of.

video: https://www.dropbox.com/s/hjhvmbxwduiraay/shotwell1.ogv?dl=0