In the quoted line you see
‘REF XXX’
But I think the program source code should rather be typed as:
'REF XXX'
Please find that the ' characters in the text you pasted were silently converted to a ‘ or a ’ by Discourse (the Wiki engine used for this forum site).
' is named as ‘APOSTROPE’ (in UNICODE U+27)
‘ is named as ‘LEFT SINGLE QUOTATION MARK’ (in UNICODE U+2018)
’ is named as ‘RIGHT SINGLE QUTATION MARK’ (in UNICODE U+2019)
In all of program source codes we use the APOSTROPH.
Discourse silently converted the APOSTROPH to other characters.
So you got confused.
If you carelessly copy and past a LEFT SINGLE QUOTATION MARK into your program source, then you will encounter an error
Invalid character at position: 4 of value
That’s the reason why @himanisaxena19 got the error