Checked with the "File associations" and "Files highlighting and sort groups" menus.

• /\.jpe?g$/i works.
• /\.(jpe?g)$/i works.
• /\.(jpe?g|webp)$/i gives "File-mask string contains errors" warning, and can't be applied.

Or maybe there is some other way except PCRE to make far2l consider file masks as case-insensitive?