Expand description
Strict JSON finder.
Finds the first valid JSON value rooted at an object ({...}) or array
([...]) in the input. Bare numbers, strings, and literals are intentionally
not surfaced — they’re too easy to false-positive on prose.
Validation follows RFC 8259: it checks string escapes (including \uXXXX
with UTF-16 surrogate pairing), number shape, and that the only allowed
JSON literals are true, false, and null. Inputs whose braces happen
to balance but contain garbage ({not really json}) are rejected.
Documents nested deeper than MAX_DEPTH (256 levels) are refused outright:
they yield no match at all rather than an arbitrary inner fragment.