Append check function with _Strict?

Question

An answer in this question mentioned you can use ISDATE_STRICT in an array formula, and it worked.
I searched all over and could not find a reference to the use of _STRICT anywhere.

1. Does this apply to all "IS" check functions?
2. What exactly is it doing?

Answer 1

Yes, unfortunately, I also don't see any articles/documentations about this one except this.

The link above is a list of sheets formulas, we can see _STRICT on 3 formulas.

ISDATE_STRICT, ISDATETIME_STRICT, ISTIME_STRICT

1. The link above does answer your first question, it does not apply to all functions IS functions.
2. Based on their behaviors, I guess that they strictly check if the value is treated and valid as date/time/datetime in sheets itself. Simply passing string as parameter will yield FALSE.

Testing:

Note:

• I have a hunch why 25:02:00 for ISTIME_STRICT is still valid for time even though it goes past 24. Sheets automatically converted that value from the inputted value 25:02 thus suggests that what sheets treats as date/time/datetime, will always yield TRUE for those functions.
• To test the hypothesis above, I inputted November 31, 2021 1:00 manually and it wasn't converted into 11/31/2021 01:00:00 automatically, it was still the same cell value because it wasn't treated as datetime variable by sheets, thus returning FALSE