Proposed Syntax

$_internalSchemaPatternProperties imposes sub-schemas on fields of an object, based on whether or not they match a regex. It has the following form:

{ $_internalSchemaPatternProperties: <regex-expression-list> }

<regex-expression-list> has the following form:

[
    {regex: <regex>, expression: <MatchExpression>},
    ....
]

To constrain a subobject, wrap it in an $objectMatch:

{ <field>: $objectMatch: { $_internalSchemaPatternProperties: <regex-expression-list> } }