Creating a string pattern to specify a single letter character, which is lowercase, without using LowerCaseQ

I'm running quite an old version of Mathematica: version 9.0. I wish to create a function oneLetterLowerCase that takes a string str as input and determines whether the string contains exactly one letter, which is lowercase.*

In other words, oneLetterLowerCase[str] should return

• True if str contains exactly one letter, which is lowercase; and
• False otherwise.

I find it easy to use LowerCaseQ to determine whether a character is a lowercase letter, because nonletter characters are considered neither lowercase nor uppercase:

myCharList = {"a", "\[Omega]", "A", "\[CapitalOmega]", "1", "!", "-", "_"};{#, LowerCaseQ[#], UpperCaseQ[#]} & /@ myCharList(* {  {"a", True, False}, {"\[Omega]", True, False}, {"A", False, True},  {"\[CapitalOmega]", False, True}, {"1", False, False}, {"!", False, False},  {"-", False, False}, {"_", False, False}}} *)

Thus I can use LowerCaseQ in a pattern test within StringCount (which takes a string pattern as its second argument) to count the number of lowercase letters in the string str:

myStringTestCaseList = {"123-_aB", "!!123-_a456", "123-_ab"};oneLetterLowerCase[str_String] := StringCount[str, _? LowerCaseQ] == 1;oneLetterLowerCase[#] & /@ myStringTestCaseList(* {True, True, False} *)

I think that the above definition for oneLetterLowerCase gives the intended results and is robust.

But, suppose I do not wish to use LowerCaseQ in a (string) pattern test as I did above. How can I create a (string) pattern that doesn't use LowerCaseQ? Is there a way to more directly specify a lowercase letter in a (string) pattern?

I can use LetterCharacter in a (string) pattern that specifies the string contains at least one letter character:

myStringTestCaseList = {"123-_aB", "!!123-_a456", "123-_ab"};StringMatchQ[#, ___ ~~ LetterCharacter ~~ ___] & /@ myStringTestCaseList(* {True, True, True} *)

But how do I specify that there is exactly one letter character and that it is lowercase? Is this possible without the use of LowerCaseQ?

It seems to me there is probably some relatively straightforward way to specify lowercase letters in a "pattern-native" way (i.e., without using LowerCaseQ), but so far I'm not seeing it in the documentation for version 9.0.

Please note that Mathematica 9.0 is quite an old version and doesn't contain higher-level functions, such as Alphabet, introduced in more recent versions. (As of the fourth quarter of 2024, the most recent Mathematica released is 14.1.)