here is an example
http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuKhEpot8pqlDAr5GSZPKKaWiLd0sLAZcKe22lFoIL0MbwkgOl0AWXipap894e5BVIaUGIiUOF4TTEpidAuM2ebIWV6fCNcrjJ1xOb9JKaiJCd68_e7v3JawGURLS3gbvAK0x0G00
Here you have MyA without double quotes, and the code works fine. However, if you want to put a space inside the participant name (like I described initially: "My A"), you must put the name into double quotes, and, hence, you need a way to escape those in my example (that is, when you embed a sequence inside a note)