Nonsense writer penning start of poem getting positive response - a regular occurrence (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[ P <oem> (“start of” means first letter only) + YEA (=positive response, affirmative vote)] in LEAR (=nonsense writer, i.e. Edward Lear and his nonsense verse); since it happens once every four years, a leap year can be described as “a regular occurrence”!