Attribute values quoting

I clarified double-quoting of attribute values as follows:

A list of feature attributes in the format tag=value. Multiple tag=value pairs are separated by semicolons. URL escaping rules are used for tags or values containing the following characters: ",=;". Spaces are allowed in this field, but tabs must be replaced with the %09 URL escape. Attribute values do not need to be quoted, and while the use of quote characters is not dis-allowed, the quotes should be included as part of the value by parsers and not stripped.