I discovered that when using th Advanced Search, the comparison of a text Search, against a Selection field's contents, is case-sensitive.
For example the Advanced Search below, is supposed to retrieves entries that have the value "hq" in the "Point Of Use" field.
I notice that it only catches entries if the value of their "Point Of Use" field is EXACTLY the string "hq". If an entry's "Point Of Use" field value is "HQ", that entry is not listed in the view output(!).
For example here is my view output based on the query above. Note that the result is rather strange. I expected it to retrieve all rows where the "Point Of Use" is "HQ". However, there are entries that are retrieve that do not meet the "Point Of Use" is "HQ" criteria (see the red 'X's).
If I then proceed to create a new query (Advanced Filter) with these setting (observe the "HQ" in capitals letters:
The resultant View output correctly lists entries that have the value "HQ" inside their Point of Use field. If an entry has the value "Hq" in its Point Of Use field, that entry will not be listed in the output. A not so user-friendly (an inaccurate) result.
From this, I can conclude that string search value in the Search Options form will only work if the comparison is case-sensitive. This makes it hard for the user. The Advanced Filter becomes more tedious for the user because he must type an exact case value inside the text box containing the search string inside the Search Option form. For example, to catch entries that have the value "HQ Owned Centre" in a field, the user must be careful to type the exact same value of "HQ Owned Centre" inside the text input box. Otherwise a value like "Hq owned centre" will fail cause the comparison to fail.
By right, the comparison should be non-case sensitive so that the user need not match the search string with the exact case-sensitive actual field values (which means less work for the user - more userfriendly).
I have tested an Advanced Filter by searching a string value against the values of a Text field. In the case of a Text Field, the comparison is non-case sensitive which is the preferred way (more user-friendly) of comparisons.
Below is the Selection field named "Point Of Use" and its settings and option values that I used in my work: