When you edit the expression in the expression editor. One of the functions SEARCH offers you to supply the arguments for "Find text", "Text to Search", "Start position".
This is confusing and can cause the incorrect usage of function. The suggested would be:
Needle *
Haystack *
Start Position
Even better would be to include an example:
Needle * " "
Haystack * ${UserName}
Start Position 1
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