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use of .text to create an .inc file

Category: Software
Product Number: LTspice
Software Version: LTspice 24.0.12
Here's the issue in a few lines (I also posted this on groups.io)
 
I declare these text substitutions:
 
.text filter1 = "fir1orig"
.text incsub1 = "sub for "
.text dottxt = ".txt"
.text file1 = incsub1 + filter1 + dottxt
 
I reckon file1 should equal:
 
sub for fir1orig.txt
 
If I now put
 
.inc |file1|
 
I get an error:
 
Could not open include file "|file1|"
 
but
 
.inc "sub for fir1orig.txt"
 
works fine in the sim because that file is there.
 
Am I garbling the syntax, expecting .text to do something it won't, or both, or neither?  I've tried various combos of pipe, quote marks and partial string definition, always get an error.