fix: make the comment clear more.

extension-src/dataTool/gexf.js

@@ -17,8 +17,12 @@
 * under the License.
 */
 
-// GEXF File Parser
-// http://gexf.net/1.2draft/gexf-12draft-primer.pdf
+/**
+ * This is a parse of GEXF.
+ *
+ * The spec of GEXF:
+ * https://gephi.org/gexf/1.2draft/gexf-12draft-primer.pdf
+ */
 
 import * as zrUtil from 'zrender/src/core/util';
 

src/component/tooltip/TooltipContent.js

@@ -219,7 +219,9 @@ TooltipContent.prototype = {
         var el = this.el;
 
         el.style.cssText = gCssText + assembleCssText(tooltipModel)
+            // Because of the reason described in:
             // http://stackoverflow.com/questions/21125587/css3-transition-not-working-in-chrome-anymore
+            // we should set initial value to `left` and `top`.
             + ';left:' + this._x + 'px;top:' + this._y + 'px;'
             + (tooltipModel.get('extraCssText') || '');