Use non-normative language in beginning of section 3.1

[Kyle Larose]

Alvaro writes

(5) §3.1: "An Identifier MAY be a field...Or, an Identifier MAY be an ephemeral
property..."   s/MAY/may  These seem to be statements and not normative
statements.

These are examples of where an identifier could come from, not really an exhaustive list
of possibilities.

Replace the two 'MAY' occurrences with 'could'.