[chaley]

Originally Posted by Thomas_AR

I added simple the Tag "MAS" (Multi Author Series) to "tags", than using:

program:

# return separator+authors if no Multi Autor Serie (MAS) is found, or return empty
various_authors=in_list(
	field('tags'),
	'&',
	'MAS',
	'',
	 strcat(' - ', field('authors'))
);
[...]

..it seams to work as expected.

This works by accident. It will see MAS inside any tag, such as in MASTER. You are also using the wrong separator. Authors-like columns use '&', tags-like columns use ','.

You should use

program:

# return separator+authors if no Multi Autor Serie (MAS) is found, or return empty
various_authors=str_in_list(
	field('tags'),
	',',
	'MAS',
	'',
	 strcat(' - ', field('authors'))
);
[...]