{this-variable}|{that-variable} {later-defined} [{optional}] literal

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this-variable:
    <type>, the type for the variable value (<string>, <integer>, <url>).

later-defined:
    A variable value to be defined later, most commonly if composed of multiple parts where
    each part requires its own definition or description.

optional:
    <type>, optional values are encapsulated in [square brackets].

| (pipe character):
    OR. Separates choices from which one choice is allowed.