Tiny Validator for JSON Schema v4

tv4 is an abandoned JavaScript library designed for validating data against JSON Schema Draft v4 exclusively. Its latest release, version 1.3.0, was published in August 2015, with no subsequent updates or active maintenance. The library differentiates itself by offering synchronous, single-error validation by default, with optional methods for collecting multiple errors (`validateMultiple`) or a structured result object (`validateResult`) to better support multi-threaded environments where global state (`tv4.error`, `tv4.missing`) is problematic. It also supports `$ref` for referencing external schemas and has an optional mechanism for handling cyclical JavaScript objects. Due to its strict adherence to Draft v4 and lack of updates, it does not support newer JSON Schema drafts (like Draft 6, 7, 2019-09, or 2020-12) and is not recommended for new projects requiring modern schema features or active support.