anchor.diff:  1:2:3:
   ----
   
  +[[if_section]]
   ===== If Section
   
   A basic control flow section.
  
positive.code: 
  The dynamic parts of a template include:
  
  * *comment* 
  ** `{! This is a comment !}`,
  ** could be multi-line,
  ** may contain expressions and sections: `{! {#if true} !}`.
  * *expression*
  ** outputs the evaluated value,
  ** simple properties: `{foo}`, `{item.name}`,
  ** virtual methods: `{item.get(name)}`, `{name ?: 'John'}`,
  ** with namespace: `{inject:colors}`.
  * *section tag*
  ** may contain expressions and sections: `{#if foo}{foo.name}{/if}`,
  ** the name in the closing tag is optional: `{#if active}ACTIVE!{/}`,
  ** can be empty: `{#myTag image=true /}`,
  ** may declare nested section blocks: `{#if item.valid} Valid. {#else} Invalid. {/if}` and decide which block to render.
  
  === Identifiers
  
  
negative.code: <html>
     <body>
     {_foo}       <1>
     {  foo}      <2>
     {{foo}}      <3>
     {"foo":true} <4>
     </body>
  