I'm not an expert, but we can start with the lowest common denominator, Wikipedia:
The notation 8a or 8va is sometimes seen in sheet music, meaning "play this an octave higher than written" (all' ottava: "at the octave" or all' 8va). 8a or 8va stands for ottava, the Italian word for octave (or "eighth"); the octave above may be specified as ottava alta or ottava sopra). Sometimes 8va is used to tell the musician to play a passage an octave lower (when placed under rather than over the staff), though the similar notation 8vb (ottava bassa or ottava sotta) is also used. Similarly, 15ma (quindicesima) means "play two octaves higher than written" and 15mb (quindicesima bassa) means "play two octaves lower than written." The abbreviations col 8, coll' 8, and c. 8va stand for coll'ottava, meaning "play the notes in the passage together with the notes in the notated octaves". Any of these directions can be cancelled with the word loco, but often a dashed line or bracket indicates the extent of the music affected.https://en.wikipedia.org/wiki/Octave#Notation
That's attributed to: Ebenezer Prout & David Fallows. "All'ottava". In L. Root, Deane. Grove Music Online. Oxford Music Online. Oxford University Press.
It seems like the convention in handbells is to only double the top note (or bottom note in the bass) but reading that definition it certainly seems like it should be all the notes stemmed together.
My "Essential Dictionary of Music" (Alfred Publishing 1997) says
simply "coll'ottava: Play the written notes and those notes one
octave higher."
More recently, composers (or at least publishers) seem to be
clarifying whether they want just the top note or all the notes.
If it's not otherwise marked, I just shrug and do whatever the
conductor tells me :)
--ivan
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