title: What is the syntax called that's used for syntax highlighting?
body: <p>My apologies if this is such a trivial question for most, but it is not readily obvious to me and I can't find an answer. I am trying to understand how to code syntax highlighting for vi, but the syntax used [for the syntax highlighting] eludes me. For example, I know that</p>
  <pre><code>syn match myNumber '\d\+'
  hi myNumber ctermfg=blue
  </code></pre>
  <p>will highlight positive integers blue. What confuses me is the <code>'\d\+'</code> part. Playing around it seems that <code>\d</code> means digit and <code>\+</code> means several? But I have no idea what this syntax is called and thus can't find any documentation that could help me. I have only found links of people using it without explanation. I can probably decipher how</p>
  <pre><code>'[-+]\=\d[[:digit:]]*\.\d*[eE][\-+]\=\d\+'
  </code></pre>
  <p>means 'positive and negative numbers with decimals and exponents', but if I am to make more complex highlighting I don't know where to begin. Does anybody know of any documentation that I could use to learn this?</p>