There must be an answer to this that I've missed, but:
How do I grab the length of a string in lil? Trying to get the index of a random character in a field's text attribute.
the random[] function can select from sequences, too:
random[] # random float [0,1)
random[5] # random integer [0,4]
random[5 10] # list of 10 random integers [0,4]
random["abc"] # random character "a","b", or "c"
random["abc" 10] # list of 10 random characters "a","b", or "c"
random[("apple","pear")] # random string "apple" or "pear"
random["abcdef" -3] # list of 3 shuffled characters "a"-"f" without repeats
See the built-in functions section of the Decker Reference Manual.