Ensure tags must fit pattern before adding them

[mikemaccana]

Fixes #20

[thomasdegry]

@developit any reason why we can't merge this yet? Would be awesome to have this functionality working!

[developit]

Array.prototype.includes() is not supported in IE9, which this library targets.

[developit]

seems a shame to give up IE compat here

[mikemaccana]

We could just add a polyfill for legacy browsers. This keeps the code clean and can be deleted quickly when you finally drop IE. :^)

[developit]

I'm too obsessed with file size to go that route 😜

[mikemaccana]

Developit: it's literally only a few characters

if (!String.prototype.includes) {
  String.prototype.includes = function(search, start) {
    'use strict';
    if (typeof start !== 'number') {
      start = 0;
    }
    
    if (start + search.length > this.length) {
      return false;
    } else {
      return this.indexOf(search, start) !== -1;
    }
  };
}

See https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/includes . It's also way more readable than ye olde "if index is greater than or equal to zero".