Treatment of "%" in "filter" in YAML script

[JozefAerts]

Before I make this a ticket, there may be a simple explanation or solution ...
For rule SEND190 "part B" in the editor, we count the number of records for which OMSTRESU="%",
So our filter for that is e.g. for OMTESTCD="OWHT":

• filter:
  OMSTRESU: '%'
  OMTESTCD: 'OWHT'
  id: $owht_percent
  name: OMTESTCD # 2026-02-10
  operator: record_count

I now noticed that when there is no "%" at all in the dataset (attached), but there are two records for OMTESTCD=OWHT for which OMSTRESU is empty, also these are counted, so the result is $owht_percent = 2.
I attach the test file.
In the filter, when I replace OMSTRESU='%' by e.g. OMSTRESU='A' the empty values for OMSTRESU for OMTESTCD=OWHT are not counted with.
Currently in the rule editor, I added a test for OMORRES so that the rule always triggers, i.e.

ONLY FOR TESTING

- name: OMORRES
  operator: not_equal_to
  value: thequickbrownfox

so that we can inspect the values for e.g. $owht_percent

So my suspicion is that "%" has some "special" meaning, although, as far as I know, this is not something special for a regex.

unit-test-coreid-SENDIG190-positive-2.xlsx

[SFJohnson24]

@JozefAerts this is related to CG0531:

the % is used as a wildcard pattern.

It is described in the operation document examples:

It seems as though we need to change the wildcard symbol to something else.

[JozefAerts]

or is there a way to escape it? Like "\%"?