Cracked is a marking which starts in irregular places, and moves outwards in a branching pattern, similar to cracked glass.
This may be as extensive or minimal as you like. There's no restrictions as long as it's appropriately 'cracked'.
Cracked can either be based on the base coat colour or can be warm colours to mimic internal fire peeking through.
Regular Cracked (Kr kr) is limited to 1 colour and must be hard edged
Dominant Cracked (Kr Kr) has able to be up to 3 colours, and the inside colours may be soft or gradient edged - creating a glow or filled effect.