Why did songbook CAPITALIZE song titles in the song?

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I've had older piano/vocal songbooks (70's, 80's) say "The greatest 50 italian-american songs", and if you would say, go to "Volare" in the lyrics themselves, whenver the song title itself was in the song lyrics, it would capitalize it. Iremember that an influential magazine, "Sheet Music", did this as well.

Example:

VO-LA-RE, wo-ah wo-ah, Can-ta-re, . . . Hear, my happy heart sing"

Or another one would be:

"Come to me, I love you so, blah-blah, LA VIE EN ROSE".

As I remember, it wasn't just foreign language titles, even though above that's what I use as an example above.

Is this some kind of special usage to sheet music? Or did people capitalize titles all the time, like here on the STRAIGHT DOPE board?

[Polycarp]

It was a convention a couple or three decades ago, when quoting song lyrics, to capitalize the song title as it appeared in the lyrics. I have no idea where it came from, but I can vouch for its commonness in usage.