Authors should be aware that path names which contain a colon ":" character cannot be used as the first component of a relative URL path (e.g., "this:that") because they will likely be mistaken for a scheme name. It is therefore necessary to precede such cases with other components (e.g., "./this:that"), or to escape the colon character (e.g., "this%3Athat"), in order for them to be correctly parsed. The former solution is preferred because it does not affect the absolute form of the URL.
There is an ambiguity in the semantics for the ftp URL scheme regarding the use of a trailing slash ("/") character and/or a parameter ";type=d" to indicate a resource that is an ftp directory. If the result of retrieving that directory includes embedded relative URLs, it is necessary that the base URL path for that result include a trailing slash. For this reason, we recommend that the ";type=d" parameter value not be used within contexts that allow relative URLs.