Currently ParsedContentType allows multiple values for the same parameter name. In the header [1] it is documented:
  // Note that in the case of multiple values for the same name, the last value
  // is returned.
  String parameterValueForName(const String&) const;

However, I noticed in RFC6838 (Media Type Specifications and Registration Procedures), which defines the MIME types for media, has the following statement:
  It is an error for a specific parameter to be specified more than once.

RFC2045, which is referenced by ParsedContentType, does not say anything about multiple parameters with the same name. So it is possible that other MIME specifications do allow multiple values for the same parameter name. It would be nice if this was detectable.


[1] https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/network/ParsedContentType.h?l=61