A multi-type schema is a schema where the `type` keyword is an array of possible types instead of a single type. For instance, `[ 'object', 'string' ]` would allow objects or string values.
In [46249] basic support for these schemas was introduced. The validator would loop over each schema type trying to find a version that matched. This worked for valid values, but for invalid values it provided unhelpful error messages. The sanitizer also had its utility restricted.
In this commit, the validators and sanitizers will first determine the best type of the passed value and then apply the schema with that set type. In the case that a value could match multiple types, the schema of the first matching type will be used.
To maintain backward compatibility, if unsupported schema types are used, the value will always pass validation. A doing it wrong notice is issued in this case.
Fixes#50300.
Props pentatonicfunk, dlh, TimothyBlynJacobs.
git-svn-id: https://develop.svn.wordpress.org/trunk@48306 602fd350-edb4-49c9-b593-d223f7449a82
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