From Canonist Ed Peter's web site In Light of the Law:
That the general law of abstinence from meat on Fridays (c. 1251) does not bind on "solemnities" (like the Solemnity of St. Joseph, per c. 1246.1 and the Gen. Norms for the Lit. Year and Calendar) is so obvious that few commentaries bother to say "If the Solemnity of St. Joseph falls on a Friday, even in Lent, one need not abstain from meat." Nevertheless, the exemption from abstinence on solemnities is patent, and one need not bother pastors or bishops for a dispensation before enjoying a pepperoni pizza this Friday. Nuf said.
Read the rest at his blog, with a bit of commentary.