code: function DOMHelper(_document) {
      this.document = _document || document;
      if (!this.document) {
        throw new Error("A document object must be passed to the DOMHelper, or available on the global scope");
      }
      this.canClone = canClone;
      this.namespace = null;
  
      installEnvironmentSpecificMethods(this);
    }
docs: /*
  A class wrapping DOM functions to address environment compatibility,
  namespaces, contextual elements for morph un-escaped content
  insertion.
  
  When entering a template, a DOMHelper should be passed:
  
  template(context, { hooks: hooks, dom: new DOMHelper() });
  
  TODO: support foreignObject as a passed contextual element. It has
  a namespace (svg) that does not match its internal namespace
  (xhtml).
  
  @class DOMHelper
  @constructor
  @param {HTMLDocument} _document The document DOM methods are proxied to