EXFO FTB-500 Guía Del Usario página 368

Data Types
Applicable Data Types for Input—IEEE 488.2
<STRING PROGRAM DATA>

This data type will be used for strings containing 7-bit ASCII characters
that have to be enclosed in either single- or double-quotes delimiters.
If a string needs to contain a character that is exactly the same as the
delimiter, make sure to double the character to avoid syntax errors.
Examples: "SCPI Commands", 'SCPI Commands', "SCPI 'Commands'",
'SCPI "Commands"', "SCPI ""Commands""", 'SCPI ''Commands'''
360
'
'
"
"
'
<inserted >
<non single
quote char>
"
<inserted >
<non single
quote char>
'
"
FTB-500