Free Hero Mesh

  %    Successful match; the result is the length of the matched slice.

A "delimited string" in this block is delimited by any printable
character on both sides (except a character with code less than 32).

(The above list of pattern codes maybe it isn't explained very well;
hopefully someone else know how to improve it better.)

After the instructions for a % block is executed, there should be only one
or zero items on the stack. If none, then this one is ignored; if there is
one, then it is added to the accumulation. For all three kinds, if only one
value is given it can use that even if it is not a number.

After the instructions for a : block is executed, the possible cases are:

* The stack is empty, or contains only a mark: The result is null.

* The stack contains only a number: The result is that number. It will be
treated as signed or unsigned according to the column type.

* The stack contains one or more items, of which the first (bottom) one is
a string: Concatenates all of them together, which can be strings, numbers
(treated as unsigned), or classes. All formatting codes of strings will be
stripped, so that the result will be a unformatted string.