Finding a file with a specific string

Content Authoring
1

Here’s what I have so far, please tell me what I am doing wrong

pathname of descendant whose (line of it contains “AngerIsAGift”) of folder “c:\temp”

2

Firstly, be very careful with descendants - it could be very slow.

That said:

pathnames of descendants whose (exists lines containing "xxx" of it) of folder "c:\temp"

or if you want to be case insensitive

pathnames of descendants whose (exists lines whose (it as lowercase contains "xxx") of it) of folder "c:\temp"