Filtering Syntax

I just started using the new version of MP3Tag and I'm confused by the new filter function. Sometimes I can get it to work but not always. How would can I filter for File Extension (extension=flac for instance). Can I do a combined filter (genre=rock and artist=Beck)?

try the following line:
genre MATCHES rock AND artist MATCHES Beck

it is absolutely vital that you write the keywords in CAPITALS. A "matches" it not recognized but a "MATCHES" is.
If you have more complicated filter strings with blanks then use "" to delimit them:
artist MATCHES "Jeff Beck"
Does this help?

MATCHES is for regular expressions. It works but it might be safer to use IS or HAS for simple queries.
Also read

Hi dano,
I tired my best ... but apparently you are still better. What may be the dangers of using MATCHES (besides them causing fire - just kidding)?
Would it be simpler to reduce the filter syntax to just one keyword that is suitable for all cases: simple queries and more complex ones? But I am eager to hear about the dangers. Would you, please?

Regex has a bunch of characters that have a special meaning that many users probably won't know.
This might produce errors for them.
I'd just avoid regex unless it is really needed.

Thanks, I'll use CAPITALS. Is there some documentation somewhere?