Merge pull request #392 from MidhunSureshR/documentation

Documentation for Hydrogen

documentation/UI/index.md

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+# Index for UI code
+
+1. [Rendering DOM elements](./render-dom-elements.md)

documentation/UI/render-dom-elements.md

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+tldr; Use `tag` from `ui/general/html.js` to quickly create DOM elements.
+
+## Syntax
+---
+The general syntax is as follows:
+```js
+tag.tag_name({attribute1: value, attribute2: value, ...}, [child_elements]);
+```
+**tag_name** can be any one of the following:
+```
+    br, a, ol, ul, li, div, h1, h2, h3, h4, h5, h6,
+    p, strong, em, span, img, section, main, article, aside,
+    pre, button, time, input, textarea, label, form, progress, output, video
+```
+
+<br />
+
+eg:
+Here is an example HTML segment followed with the code to create it in Hydrogen.
+```html
+<section class="main-section">
+    <h1>Demo</h1>
+    <button class="btn_cool">Click me</button>
+</section>
+```
+```js
+tag.section({className: "main-section"},[
+    tag.h1("Demo"), 
+    tag.button({className:"btn_cool"}, "Click me")
+    ]);
+```
+<br />
+
+**Note:** In views based on `TemplateView`, you will see `t` used instead of `tag`.  
+`t` is is `TemplateBuilder` object passed to the render function in `TemplateView`.
+Although syntactically similar, they are not functionally equivalent.  
+Primarily `t` **supports** bindings and event handlers while `tag` **does not**.
+
+```js
+    // The onClick here wont work!!
+    tag.button({className:"awesome-btn", onClick: () => this.foo()});
+
+    render(t, vm){
+        // The onClick works here.
+        t.button({className:"awesome-btn", onClick: () => this.foo()});
+    }
+```