Any chance of implememting the display of multiple spaces in a tag.
Something like Name Mangler does on the Mac.
You could use a filter with e.g.
%title% HAS " "
I was thinking in the main window so you could quickly identify multiple spaces, spaces at the start and end of a tag.
This would be only one of the many possibilities of untidy data. Apostrophes (and all their invalid variations) would be a similar problem, lower case following a full stop, and probably many more.
And for these cases there is the filter that is user-defined and may cater for all the individual spaces.
In collections with several thousands of files, a visual inspection would simply be unfeasible or extremely time consuming. The filter works in seconds.
The following step would be, I assume some method to remove these characters or replace them - so it would require an action as stepping through all the files manually would, again, be extremely time-consuming whereas the action would finish the job in minutes, if not seconds.
There is a section in the FAQs on how to remove leading and trailing spaces: