Thanks and a request for shell quoting explanation

[LosAlamosAl]

Regarding 2021-03-15-how-to-write-an-aws-cli-script-part-i-patterns.md:

First, you saved my bacon with this post. Thanks!

Second, it would be useful to have a note describing the shell-fu that enables this:

'StackResourceSummaries[?ResourceType==`'"$resource_type"'`].PhysicalResourceId'

I can't decipher the quoting that's going on in that parameter substitution of $resource_type!