The package provides the \collect@body command (as in amsmath), as well
as a \long version \Collect@Body, for collecting the body text of an
environment. These commands are used to define a new author interface to
creating new environments. For example: \NewEnviron{test} wraps the
entire environment body in square brackets, doing the right thing in
ignoring leading and trailing spaces.

Homepage:
https://www.tug.org/texlive/
