[reSIProcate] tel: URI encoding in HTML

["Daniel Pocock" <daniel@xxxxxxxxxxxxxxxxxxxxx>]

When representing a tel: URI in HTML, e.g. for the sipdial demo, is it
necessary for the + to be % encoded?

<a href="tel:+442071358378">

or

<a href="tel:%23442071358378">

Many examples show it without encoding, however, some applications,
particularly web applications, seem to automatically encode any + in any
URI, regardless of URI scheme.

The RFC 3966 says the following:

  If the reserved characters
   "+", ";", "=", and "?" are used as delimiters between components of
   the "tel" URI, they MUST NOT be percent encoded.  These characters
   MUST be percent encoded if they appear in tel URI parameter values.

Is the + at the start of a phone number considered to be a delimiter or
part of a URI parameter value?  I don't believe it fit's into either
category, as it is not a delimiter, and parameter values only follow a
question mark.