[DOC] add some information on variables and t-call

closes #540

src/misc/portal.ts

@@ -137,8 +137,7 @@ export class Portal extends Component<any, any> {
     }
     this.__checkVNodeStructure(vnode);
     const shouldDeploy =
-      (!this.portal || this.el!.contains(this.portal.elm!)) &&
-      !this.doTargetLookUp;
+      (!this.portal || this.el!.contains(this.portal.elm!)) && !this.doTargetLookUp;
 
     if (!this.doTargetLookUp && !shouldDeploy) {
       // Only on pure patching, provided the

src/qweb/qweb.ts

@@ -650,7 +650,7 @@ export class QWeb extends EventBus {
       if (!name.startsWith("t-") && !(<Element>node).getAttribute("t-attf-" + name)) {
         const attID = ctx.generateID();
         if (name === "class") {
-          if (value = value.trim()) {
+          if ((value = value.trim())) {
             let classDef = value
               .split(/\s+/)
               .map(a => `'${a}':true`)