Question about mini libraries people put in their yards….

a couple houses in my neighborhood have mini libraries you can take books from. i've grabbed probably 10 for my daughter.

my husband and i were talking about a book i grabbed today and he said, 'oh, did you take the other books back and grab new ones?'

aaaand i didn't realize you took them back!! i've been keeping them this entire time.

so my question is what are the rules surrounding the mini libraries? do they work like regular city libraries where you return the books? do you keep them? can you add more books to the library??

i'm so confused! someone please help!