SVG.Doc = SVG.invent({
  // Initialize node
  create: function(element) {
    if (element) {
      // ensure the presence of a dom element
      element = typeof element == 'string' ?
        document.getElementById(element) :
        element

      // If the target is an svg element, use that element as the main wrapper.
      // This allows svg.js to work with svg documents as well.
      if (element.nodeName == 'svg') {
        this.constructor.call(this, element)
      } else {
        this.constructor.call(this, SVG.create('svg'))
        element.appendChild(this.node)
        this.size('100%', '100%')
      }

      // set svg element attributes and ensure defs node
      this.namespace().defs()
    }
  }

  // Inherit from
, inherit: SVG.Container

  // Add class methods
, extend: {
    // Add namespaces
    namespace: function() {
      return this
        .attr({ xmlns: SVG.ns, version: '1.1' })
        .attr('xmlns:xlink', SVG.xlink, SVG.xmlns)
        .attr('xmlns:svgjs', SVG.svgjs, SVG.xmlns)
    }
    // Creates and returns defs element
  , defs: function() {
      if (!this._defs) {
        var defs

        // Find or create a defs element in this instance
        if (defs = this.node.getElementsByTagName('defs')[0])
          this._defs = SVG.adopt(defs)
        else
          this._defs = new SVG.Defs

        // Make sure the defs node is at the end of the stack
        this.node.appendChild(this._defs.node)
      }

      return this._defs
    }
    // custom parent method
  , parent: function() {
      return this.node.parentNode.nodeName == '#document' ? null : this.node.parentNode
    }
    // Fix for possible sub-pixel offset. See:
    // https://bugzilla.mozilla.org/show_bug.cgi?id=608812
  , spof: function(spof) {
      var pos = this.node.getScreenCTM()

      if (pos)
        this
          .style('left', (-pos.e % 1) + 'px')
          .style('top',  (-pos.f % 1) + 'px')

      return this
    }

      // Removes the doc from the DOM
  , remove: function() {
      if(this.parent()) {
        this.parent().removeChild(this.node);
      }

      return this;
    }
  }

})