Text warp (skinparam wrapWidth 30) works fine in note and rnote but it doesn't work inside hnote.
http://www.plantuml.com/plantuml/uml/lPEzYiCm48JxVOfft9t1SCrXZk17S9Soh7wmXIFPhANazQC4WkqwH6gaqIpxmJBRhP4b9d-b9TzEkuL311-KEYXDdE8SabTMQ9rSo2Pxz5j9pyQuCE2lsVbtuUNiJ1pnsn2ZFa6XzUj0OOuMyyqA62sghNa5FfnF98rbC586iwFyg49J-of8Ie7KCtdwbJoGs9Wa8Bylh2TY_DSrCltzqTbWycey0000
@startuml
participant a
participant b
participant c
autonumber
skinparam ParticipantPadding 80
skinparam wrapWidth 30
a -> b :msg
note over a : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
hnote over a : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
rnote over a : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
note over a,b : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
hnote over a,b : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
rnote over a,b : %autonumber% aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaaa
b -> c :msg
return msg_ack
a <-- b :msg_ack
@enduml