There is no enjambment in song

 I  had a significant idea last night: there is no enjambment in song. 

With the necessary qualifications. In other words, the syntactic phrase does not continue into another musical phrase (in the normal course of events). When it does, I perceive it as a mistake, or as something jarring, at the very least.  See this version of Claudio poems "Siempre será mi amigo..."  He just stops at the end of a line and awkwardly starts again, with no sense of the continuity of the syntax.  "verdadera ... amistad."  True / friendship. In spoken recitation, this would require a very brief pause, if anything.  

So instead of saying "there is no enjambment" you might say, "there shouldn't be enjambment" in song. Of  course, that is assuming one wants a decently defensible prosody in text setting. 

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On of the most insightful things I've read on musical prosody (the pairing of music and words) is by Sondheim, in the introduction to his collected lyrics. Not because I share his opinions, or even like, particularly, his songs, but because he has worked out a philosophy of what he wants to do, what works and doesn't, with admirable clarity. You can see his perspective immediately, and he speaks authoritatively. It provides a jumping off point for any other ideas one might have.