typeset -A foo=([one]=bar [two]=baz [three]=quux)
typeset -p foo

foo+=zero
typeset -p foo

foo+=([four]=four)
typeset -p foo

typeset -ia iarr=(2 2 3)
iarr+=1
typeset -p iarr

iarr+=(4 5 6)
typeset -p iarr