I don't know for sure but I think it uses current record in the table not the first one. Here's the test

CREATE CURSOR testxx ( c1 C(20))
INSERT INTO testxx VALUES ("Line 1")
INDEX ON STRTRAN(c1, " ", "") TAG c11  && No error
INSERT INTO testxx VALUES ("")
INDEX ON STRTRAN(c1, " ", "") TAG c11  && Error "Invalid key lenght"
GO TOP
INDEX ON STRTRAN(c1, " ", "") TAG c11  && No error

>>This index will be used by Rushmore. However, it isn't relable because the lenght of the index key depends on the record VFP uses to determine it. If table is empty, you wouldn't be able to create such index at all.
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>Your second point makes the case for me!
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>As regards the length of the index key... does INDEX ON operate the same way that SQL-Select does as to the way SQL uses the first (qualifying?) field's content to establish the length of all output of the field? It seems most unlikely to me that INDEX ON would operate that way.
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>thanks