Questions of a beginner

I am coming to understand Mp3Tag bit by bit but are still struggling with probably simple problems:

  • when a tag is empty I cannot fill it other than to format it and thus fill it with the content of another tagfield and then change it to whatever it should be. When then replacing with regex such a string (.*) by the word I want (e.g. in the tag Genre the word Organ) it becomes OrganOrgan.

  • I don't quite get the idea of using the guessing action: when the title is e.g. Composer - Composition - Part how do I get the first two in their respective tags. Can this be done in one go?

  • when I want to replace e.g. Symfony No.1 by Symfony No. 1 (space after No.1). I use the regex (.)No.(.) and replace by $1No. $2 but then the number disappears.

If a field is empty, it is not there.
If you want to get a certain value into a field you have the follwing options:

  • Enter it in the tag panel and press Ctrl-S to save
  • Open the extended tags dialogue (Alt-T) and create a new field (New button)
  • use an action of the type format value.

This type of action works similar to the Convert>Filename-Tag function:
You determine the field which has all the data.
Then you enter the target fields and the pattern that lets assign the data to a certain field.
In the example the source would be TITLE
The Guessing pattern would be: %composer% - %composition% - %title%

As you want to replace one text constant with another it is not necessary to use a regular expression. A simple replace is enough: Replace No. with No.
In respect to the expression, I cannot see anything wrong.
You can check that in teh function Convert>Tag-Tag
Enter: $regexp(Symfony No.1,(.*)No.(.+),$1No. $2)