test if first char in string is letter

What is the quickest way to test if the first char in a string is a letter
(case does not really matter)?

BG: I have a situation where the 4th entry (in a table structure) is supposed
to be either empty or number, but due to styling issues in Frame sometimes a
string may appear (very rare). I want to remove the string to the 5th entry
(combine both the 4th and 5th into the 5th entry) and leave an empty 4th
entry. I could do it long hand : lower-case(substring(child::*[4], 1, 1)) =
'a' or lower-case(substring(child::*[4], 1, 1)) = 'b'etc but that seems a bit
excessive. I'm doing this in an

<xsl:template match="para[string-length(normalize-space(.)) = 0 and
ancestor::*/@cols = '5']">

Would like to add a test after the @cols check.

Any insight would be appreciated.

Thanks

Marijan (Mario) Madunic
Publishing Specialist
New Flyer Industries

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