quote_and_expand.txt

export TMP='"hello wolrd"'

[0]"hello
[1]world"

"$TMP yo"
^^< > <>^
QuoteDollarWord WordQuote

""hello word" yo"
^<    > <   > <>
QuoteWord Word WordQuote

The real quote are defined as TOKEN_QUOTE while added quote by a var expansion will be classified as a TOKEN_STRING
then you group from one TOKEN_QUOTE to another TOKEN_QUOTE