Partially mask a string by replacing a given number of characters with a
fixed character. Masking can start from the beginning or end of the
string. This can be used on data of any type (numbers, longs, and so on)
and when de-identifying structured data we'll attempt to preserve the
original data's type. (This allows you to take a long like 123 and
modify it to a string like **3.
Number of characters to mask. If not set, all matching chars
will be masked. Skipped characters do not count towards this
tally.
When masking a string, items in this list will be skipped when
replacing. For example, if your string is 555-555-5555 and you
ask us to skip - and mask 5 chars with * we would produce
**\ -\ 55-5555.
