The text a non-string argument converts to stays rooted while the parse runs, so a
collection still counts it. A property name read from the text is charged to the heap
until its property is defined. Boolean.prototype.toString and valueOf are added, so a
Boolean object writes `true` or `false`. The json2 sample no longer includes U+2028:
the polyfill escapes it and section 15.12.3 does not.
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