{{str_sub|text|start|length}} = Substring of text starting at start and containing length characters. Base 0: the first character is numbered 0, and so on, e.g. {{str_sub|20090624130510|8|2}} returns the 2 characters starting at the 9th, i.e. "13"

start + length must be less than 50. Only operates on a limited character set.

The character set is A-Z, a-z, 0-9, space and !@#$%^&*().,<>:;[]'"?/\{}~`=-|+_♣♦♥♠. (Obviously | and = will have to have been input as {{!}} and {{=}}.)