https://resources.infosecinstitute.com/topic/ida-cross-references-xrefs/
XREF , "...After the arrow, there’s also a single letter..."
- letter ‘j’ denotes the jump
- letter ‘p’ denotes the function call
DATA XREF, "...letters assigned after the arrow ..."
- letter ‘w’ denotes that the location is being written to
- letter ‘r’ denotes that the location is being read from
- letter ‘o’ denotes that the address of the location is being taken from it
