What are the rules for an elegy? I can not find any

Elegy in the beginning was related to a particular kind of
prosodic or metrical structure that was called the elegiac rhythm but now it is regarded
as a thematic notion. It is a lyric poem/song of lament, mourning the death of a near
one or beloved or at a deeper level even a phenomenon, an emotion, a state of the
matter, an ideology or an era.

Some of the conventions of
pastoral elegy are--

1. The mourning in the form of a
dialogue between two shepherds.

2. The active participation
of rural nature in the mourning.

3. The idealization of the
dead figure of the shepherd.

4. The description of some
funeral procession or other commemorative measure.

5. The
rather Christian conclusion where the elegiac emotions of mourning and melancholia are
undercut by the Christian rhetoric of belief where death is a happy occasion, a true
homecoming of the soul after the finite sojourn of mortal life on the earth or a reunion
with the God. This divine optimism is made to counter the elegiac mood in this final
movement of transcendence.