http://tools.ietf.org/html/rfc2616#section-3.7 says that "Linear white space (LWS) MUST NOT be used between the type and subtype, nor between an attribute and its value" whereas http://tools.ietf.org/html/rfc2616#section-3.6 says "parameter = attribute "=" value".

NOTE : The white space between the word attribute and the equal to sign and similarly, equal to sign and the word value.

In the Example section of http://dev.w3.org/2006/webapi/FileAPI/#constructorParams an instance is given of the call :

var b = new Blob(["foobarbazetcetc", "birdiebirdieboo"], {type: "text/plain;charset=UTF-8"});

So, I assume |charset = UTF-8| should throw an error |charset=UTF-8| should not. Only two cases are possible : Either the example is wrong or the algorithm isn't clear enough.

Expectation : Either a more clear language used in the IETF specification to explain the ABNF for media-type.