The renderer code is [here](https://github.com/johnallsup/pt2_public/blob/master/root/.php/ptmd.php).

# Specials
There are two types of specials: *block* and *inline*. Inline extends the `[[inline link]]` notation,
noting that an href containing a colon is invalid, and so if `:` occurs in it, it is a special.

## Inline Specials
For example `[[youtube:N7GoTb5L5gM]]` embeds [this](https://www.youtube.com/watch?v=N7GoTb5L5gM)
video thus: [[youtube:7QVWjNAPxbQ]]

It removes leading and trailing spaces, so `[[youtube: 7QVWjNAPxbQ ]]` works. But it
rejects invalid id's such as [[youtube:7QVWjNAPxbxQ]].

We add inline specials to PTMD by adding methods named
```
  function special_inline_flibble($what,$args) {...
```
The `$what` in `[[flibble:hexvision]] is the `flibble` bit, essentially whatever is before the first `:`, and the `$args` is everything afterwards. Simples.

## Block Specials
Here we reuse fenced code blocks. Ordinarily, a block fenced by backquotes
````random
```python
like this
```
````
will be formatted as a code block with in this case the language set to Python.
By adding methods
```
  function special_block_duolingo($what,$options,$content) {...
```
for example, we can then have blocks like
````random
```duolingo
...
```
````
have some custom code turning them into HTML. The `$what` is the `duolingo`bit, the `$options` are whatever follows it on the `duolingo` line. Then the `$content` is everything else within the code block.