In the same way you setup keywords to search it is possible to define binary masks for each of them with the '/m' command. Here's an example of use:
[0x08048000]> /k0 lib [0x08048000]> /m0 ff 00 00 [0x08048000]> /m 0 ff 00 00 [0x08048000]> /k 00 lib
Now just use '/r 0' to launch the k0 keyword with the associated m0 binary mask and get the 3-byte hit starting by an 'l' because 'il' is ignored by the binary mask.
This case is quite stupid, but if you work with JPEGs or on ARM for example, you can type more fine-grained binary masks to collect some bits from certain headers or just get the opcodes matching a certain conditional.