Closes #809

Problem

context was normalised with a check that only jQuery objects and strings answer meaningfully:

if (!o.context || !o.context.length) {
    o.context = document;
}

A raw DOM Element has no .length, so it was dropped and the registration silently fell back to document. The menu still worked, but page-wide instead of scoped to the element that was passed, with no error and no warning.

Fix

An Element is now honoured, on the create operation, as a newly-supported shape:

} else if (operation === 'create' && o.context.nodeType === 1 && typeof o.context.length !== 'number') {

o.context stays a raw DOM node, which is what every consumer expects: $.contains(o.context, el) and o.context !== el in the trigger matching, menus[menu].context !== o.context in update, $(o.context).off(o.ns) in destroy. Nothing downstream needed to change.

Backwards compatibility

The change is deliberately additive: it only affects a shape that is ignored today and does nothing useful. Everything the old check already decided is left byte-for-byte alone, because newly honouring an ignored context does not fail loudly, it just stops a working menu from appearing outside the context element.

Kept exactly as-is, and now pinned by tests:

Two notes on the choices there:

• <form>/<select> is not carved out by tag name. The rule is "a value carrying a numeric length keeps the legacy length test", which is exactly the set of inputs the old code decided by length, window included. An empty <form> still falls back to document.
• destroy/update are excluded on purpose. For those operations context means the trigger element rather than a container (that is what $.fn.contextMenu('destroy') passes), and an Element has never been accepted there: it falls through to the "no context, no selector" branch, which tears down every registered menu. Scoping it would silently turn $.contextMenu('destroy', {context: element}) from a full teardown into a no-op, i.e. a leak.

One knock-on effect had to be handled to keep an existing call working. An ignored Element context meant the menu was also tracked in namespaces, and that map is what lets $.contextMenu('destroy', '.selector') find a registration. Honouring the context would have dropped it from that map and silently broken destroy-by-selector for exactly the callers this PR is for. So Element-context registrations keep being tracked, and the destroy-by-selector branch now unbinds from the menu's own context instead of always from document, which is where the handler actually lives now. For every pre-existing registration that context is document, so that line is a no-op change.

No jQuery 3-only APIs are used, jQuery 1.12+ stays supported.

Tests

New test/unit/issue-809-context-element.test.js. With the new branch disabled, exactly two assertions fail and everything else still passes, which is the check that the change really is additive:

• a raw Element as context scopes the registration (outside triggers do not open the menu, inside ones do)
• the same assertion in issue-731's Element case, whose comment described the unscoped behaviour as knowingly-broken and is now updated

Also asserted, passing both before and after, so a future change cannot quietly regress them:

• a menu registered with an Element context can still be destroyed by selector
• a non-empty <form> context still scopes, an empty <form>/<select> context is still ignored
• a context selector matching nothing still registers nothing
• $.contextMenu('destroy', {context: element}) still tears everything down
• jQuery object, selector string, and no context at all are unchanged

The test file is wrapped in an IIFE: Karma loads every unit test file as a plain script into one shared global scope, and the helper names collide with those in the #731 file otherwise.

Verification

• npm run test-unit: 90 passed
• npm run test-accept: 36 passed (run against a locally rebuilt dist/; dist/ is not part of this PR)
• npx eslint src/jquery.contextMenu.js test: clean

Docs

context was not documented at all. Added a ### context section to documentation/docs.md with the accepted shapes and an explicit note on the two ignored ones, flagged as deprecated so they can start scoping in a major release. Changelog entry added.