command/operation substitution enclosed with `

Command/operation substitution (following linux style back quoting an expression) would be a useful feature. Among other things, it would be useful to be able to initialize an environment variable to a result of a command or an operation, e.g.

set value=`:read-attribute(name=release-version)`

or

set value=$(:read-attribute(name=release-version))

and

echo $value
8.0.0.Final-SNAPSHOT