How to insert output of command into string in MikroTik RouterOS (scripting)

If you have a MikroTik RouterOS command such as

email_send_example.rsc
/tool e-mail send to=me@mydomain.com subject="MikroTik test E-Mail"

you can insert the output of a command such as

system_identity_get.rsc
/system identity get name

into it by using the $[...] syntax:

email_send_with_identity_example.rsc
/tool e-mail send to=me@mydomain.com subject="My identity is $[/system identity get name]"

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