Introduction Bracket glyphs

[Breanne Szilagyi]

Good Evening,

I am arranging a hymn for organ and need to indicate the recommended measures to use for an introduction.  I am looking for square brackets: the first bracket is the top and left sides of a square and the second bracket is the top and right sides. And I want to place them above the system.

Ex. https://www.lds.org/music/library/hymns/jesus-once-of-humble-birth?lang=eng

In the example, the introduction brackets enclose a few measures at the beginning of the song and then jump to the last few measures of the song.

I've searched through the Notation documentation sections that seem appropriate, and tried to do keyword searches but introduction, square, and bracket are all overloaded terms and I couldn't find a suitable substitute.  Thank you for helping a lilypond newbie.  (I'm using v2.18.2 but can switch to a higher version if needed.)

Thank you,

Breanne Szilagyi