src/Http/Formatting/RequestParser.php
public function parseParameters(
        IHttpRequestMessage $request,
        string $headerName,
        int $index = 0
    ): IImmutableDictionary {
        return $this->headerParser->parseParameters($request->getHeaders(), $headerName, $index);
    }
public function parseParameters(
        IHttpRequestMessage $request,
        string $headerName,
        int $index = 0
    ): IImmutableDictionary {
        return $this->headerParser->parseParameters($request->getHeaders(), $headerName, $index);
    }
Parses the parameters (semi-colon delimited values for a header) for the first value of a header

@param IHttpRequestMessage $request The request to parse
@param string $headerName The name of the header whose parameters we're parsing
@param int $index The
@return IImmutableDictionary The dictionary of parameters for the first value