There is no search option by category and edition right now.
I can implement both. Maybe i can do that sometime soon in priority to other things.
There are still modifiers which are not available for the quick access on the main page:
redump.org/discs/system/psx/edc/keyword/ > keyword: yes|no|unknown
redump.org/discs/system/psx/libcrypt/keyword/ > keyword: 0|1|2 (0=unknown, 1=no, 2=yes) needs optimization
redump.org/discs/system/psx/antimodchip/keyword/ > keyword: 0|1|2 (0=unknown, 1=no, 2=yes) needs optimization
redump.org/discs/title/keywords/ > keywords: separated by "-"
redump.org/discs/serial/keywords/ > keywords: separated by "-" needs a fix
redump.org/discs/offset/keyword/ > keyword: -647|0|2 needs a fix
redump.org/discs/language/keyword/ > keyword: eng|fre|ger|etc. > ISO 639-2/B
redump.org/discs/tracks/keyword/ > keyword: 1|...|99 (only cd based)
redump.org/discs/media/keyword/ > keyword: cd|dvd
redump.org/discs/media/cd/securom/keyword/ > keyword: 0|1 (0=securom data not set, 1=securom data set) needs optimization
There are some more, i will list them later as soon as i find time.
redump.org/discs/category/keyword/ > keyword: games|demos|... (only supported editions, can be lower or any case)
redump.org/discs/edition/keywords/ > keywords: separated by ","
PX-760A (+30), PX-W4824TA (+98), GSA-H42L (+667), GDR-8164B (+102), SH-D162D (+6), SOHD-167T (+12)