The first version of the routine to set the letter terms only supported the Letter taxonomy being set for posts. It would be nice to be able to run it to set taxonomy terms for other post types and letter based taxonomies.
Note: For bigram's taxonomies s-letter and b-letter this was implemented using the bigram-second-letters.php batch routine. Any changes to the oik-a2z functions may need to be reflected in the bigram code.
Issue #2 - improve batch facility to set letter terms
The logic needs to account for a first letter of &.
Since it will create a term if it doesn't exist, wp_set_object_terms() looked like a nice function to use,
Unfortunately it can't handle a value of '&' since this is not a valid slug.
It seems that we need to do the following.
This is similar to WordPress TRAC #32248 - adding a term containing "&" and renamed.
I was toying with the idea of requesting a change but opted for my own function.
The logic only works for flat taxonomies ( ie. tags not categories ).
This logic also applies when the terms are automatically set when a post is created/updated.
Issue #2 - cater for special characters like '&'
v0.0.4 2017/02/03 More work on issues #1, #2, #3