Registers are a special set of values that can be passed to your scripts from Match-IT. They typically contain information pertinent to the context the script is being invoked from. See the Register usage conventions for details. There are 32 registers, they can contain values of any Match-IT type, and they are named r01 to r32. To access them, just use their name as a field on the 'm' table, like this:

if m.r01 > m.measure(‘Metre,1’) then ...        --read
m.r02 =‘Sterling,100’)                --write