There seriously are also marriage allegations: marriage bonds and allegations exist for only couples who applied to marry by licence. They do not exist for couples who married by banns. The marriage allegation was the document in which the couple alleged (or frequently just the groom alleged on behalf of both of them) that there were no impediments to the marriage.
Generally, in a civil complaint, a plaintiff alleges facts sufficient to establish all the elements of the crime and thus create a cause of action. The plaintiff must then carry the burden of proof and burden of persuasion in order to succeed in its lawsuit.
On the other hand, defendants often plead in the alternative by listing seemingly inconsistent defenses. For example, "I did not do the crime", "if I did, I didn't know", or "even if I did know, I've got a good excuse." Such a pleading may be considered disjunctive and may be permissible.