In another rule, Eng will be replaced with something a bit complicated. In short, it attempts to replicate the style of the words in the list. Simplest way to use it would be to have a list of words (as above), and then output the rule right after (e.g. >Eng).
In long, it builds weighted trees for each letter, so if you have a list like [that than thanks], if an a is chosen at some point, then 1/3 times it will be followed by n, and 2/3 times it will be followed by n. Longer word lists will create more complex words, though too many might not produce anything useful.
The initial and terminal letters are somewhat special; if all words begin with t in your list, then all words in the output will as well. Similarly, if all list words end with an e, then all output words will, too.