Default quality value -1 isn't explained

[Ragowit]

From manual page: https://php.net/function.imagewebp

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There's no explanation what the default value of -1 in quality means. It would be great to have this explained, as in https://www.php.net/function.imageavif where it is said that if -1 is used, the default is 30 (I don't know if it's 30 in webp as well, that was just an example).

[Ragowit]

I don't know why the (imageavif) function itself have int $quality = -1 instead of int $quality = 30, but that's another issue.

[damianwadley]

Arguably a source bug: GD is perfectly capable of choosing "a good general quality / size tradeoff for most situations", and PHP already makes use of GD's default behavior for AVIF, so hardcoding 80 (just for that one format, no less) seems inappropriate.

[vrana]

It is 80 in GD too.