\section{Transformation}

The dial plan consists of lines of text, with two columns separated by
any number of space or tab characters.  The first column consists of
\header{digitString} elements as described in Appendix 7.1.14 of RFC
3015 \citenorm{rfc3015} and enhanced below, the second of the
translation, which {\MUST} be a URI valid in a SIP request. 

\motivation{We could also define an XML format. This would make it
easier to integrate into a configuration file format.}

The digit strings are enhanced by grouping indications, to allow
replacements. Group indications are enclosed in curly brackets, with no
nesting allowed. The replacement string uses the backslash character
followed by a single digit. The sequence \\verb|\\0| refers to the whole
dialed digit string.

\motivation{Parentheses already have other uses in the RFC 3015 syntax.)

For example,

\begin{verbatim}
911            sip:sos@example.com
8{xxxxxxx}     sip:+1-859-\1@example.com
xxxx           tel:\0;phone-context=+1-859-555-1234
9{1xxxxxxxxxx} tel:+\1
9011{x.}       tel:+\1
\end{verbatim}

TBD: Matching rules
