Replace the letter a with To if it is located between two groups of digits

Hi, I have this situation
I want , es, XXaYY becomes XX To YY
I thinks to use "Replace with Regular Expression]" but I can't find the syntax


Thanks for all guys

You want to replace
two characters (whatever they are)
followed by the letter
a
followed by two characters (whatever they are)

and they should become
two letters
space
To
space
two letters

Is this correct?
Do the two characters also have to be UPPERCASE and the character a lowercase?

Try Convert>Tag-Tag for TITLE :
Format string: $regexp(%title%,(.*\d\d)a(\d\d),$1 To $2)

no, I just want to replace the letter "a" with "To" if the letter a is between a group of 2 or three digit numbers (these are the Bpm).
Ex... 90a100 becomes 90 To 100
Thanks

PER-FE-CT !!!
THANKS so much

Even if your solution also works for a value with more then 2 digits, I would suggest to use
$regexp(%title%,(.*\d+)a(\d+),$1 To $2)
image

thanks again, I will study the formula to apply it in other situations

Is there a reason for including the start of the title in the match but not the end?

I've just tested it and your version which matches the start but not the end:

$regexp(%title%,(.*\d+)a(\d+),$1 To $2)

this one that only matches the numbers and "a":

$regexp(%title%,(\d+)a(\d+),$1 To $2)

and this version matching the entire title:

$regexp(%title%,^(.*\d+)a(\d+.*)$,$1 To $2)

All yielded the same result in a Convert → Tag - Tag action in mp3tag.
Personally I'd either use the easiest and shortest one that only matches the numbers and "a" or the most precise one that matches the entire string.

Visualized the version matching the entire title looks like this:

Yes, this would have been enough.
But as you see: there are so many ways to skin a cat.