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Interfaces for interop with hershel-theodore-layton/sgml-stream

Element attributes

Element::getAttribute() returns the assigned value, including explicit null, or the default when no value was assigned. The attribute maps expose only nonnull values: declared attributes go in getDeclaredAttributes(), while data- and aria- attributes go in getDataAndAriaAttributes(). The latter accepts only arraykey values; implementations may reject, cast, or filter other nonnull values as specified in the interface.

For an ordinary nullable attribute a, the same null and default rules apply to both maps:

Input for `a`	Default	`getAttribute('a')`	Entry in the appropriate map
Omitted	None or null	null	Absent
Omitted	`'fallback'`	`'fallback'`	`'a' => 'fallback'`
Explicit `'value'`	Any	`'value'`	`'a' => 'value'`
Explicit null	`'fallback'`	null	Absent
Spread source omits `a`; destination otherwise omits `a`	Destination: `'fallback'`	`'fallback'`	`'a' => 'fallback'`

Spreading copies only present map entries. In sgml-stream, declared entries are copied only when the destination declares that attribute; data- and aria- entries do not require a destination declaration. A source whose a was explicitly set to null (even over a nonnull default) cannot clear the destination's value or default. A source's nonnull default is present in its map and can be copied. For example, directly assigning a={null} suppresses 'fallback', whereas spreading that element into another element defaulted to 'fallback' preserves the destination's default. Explicit values and spreads take effect in their order in the XHP opening tag.

Behavior for unassigned @required and @lateinit attributes remains unspecified by the interface.

hershel-theodore-layton / sgml-stream-interfaces

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Element attributes