I will follow for now:
But it misses readability of .md files as first goal. Importance of telephone numbers is increasing over time (phone number first IM like Viber, global oriented SIM providers, cheap smart phones for developing countries, SIM based authorization and payment methods, and I click rel: link in Chrome installed on Windows and it launches Skype), but this can lead to invention of simplified (1 full number = 1 globally identifiable person) version of string which can be number, leading to simpler parser and other tag rather then tel:.
Right now PHP Markdown gives results I want out of tel:.
I think to follow “implement a renderer” because I need more divergence of rendering (my resume for web and for print), but “renderers” seems should be declarative like XSLT rather then imperative. Even multi language render hooks seems to hard for me.
Email and tel: could be first tests for such declarative render configuration, first will lead to email obfuscation(like in version mentioned earlier) and second to pretty print of phone number (like in PHP Markdown)