Two defects: the position keyword was matched case-sensitively with no default
(so 'BeforeEnd' inserted nothing and an invalid position silently no-oped
instead of throwing SyntaxError), and fragments were parsed inside a throwaway
<div>, so context-sensitive children (<tr>, <td>, <option>, …) were dropped.
Lowercase the position and throw SyntaxError on an unknown value; parse via a
table/select-aware wrapMap (chosen from the fragment's leading tag, falling back
to the insertion context) so rows/cells/options survive.
Fixes#495
Andrey Mnatsakanov
a663a15556