If you have little knowledge of HTML, here's an example of how web elements are organized on a page:
<title>My Web Page</title>
<h1>My Web Page</h1>
<p>This is a paragraph</p>
<a href="http://www.google.com" >Here's a link to Google</a>
<td>Row 1, Column 1</td>
<td>Row 1, Column 2</td>
<td>Row 2, Column 1</td>
<td>Row 2, Column 2</td>
If you'd like to see what this webpage would look like, you can simply copy and paste this html code into a notepad file and save it with the .html extension. Then find the file in the folder where you've saved it and double-click on it. It should open up as a webpage.
Now let's take a look at the various elements on the page. Note that each element has a beginning and ending tag. For example, the line that says "This is a paragraph" has a <p> tag to indicate the beginning of the paragraph and a </p> tag to indicate the end of the paragraph. Similarly, the title of the page has a beginning tag: <title> and an ending tag: </title>.
Notice that elements can be nested within each other. Look at the <table> tag, and then find the </table> tag several lines below it. In between the tags, you will see row tags (<tr>) and table data tags (<td>). Everything in between the <table> and </table> tags is part of the table. Now look at the first <tr> tag and the first </tr> tag. Notice that there are two pairs of <td></td> tags in between. Everything between the first <tr> tag and the first </tr> tag is a row of the table. The <td></td> pairs in the row are elements of data in the row.
Now imagine that this data is organized into tree form:
If you were going to traverse the DOM in order to get at the data in Row 1, Column 1, you'd start by finding the <table> element, then by finding the first <row> element, then you'd find the first <data> element. This is how we will use css selectors and the xpath to find elements in the next blog post.
If you'd like to find out more about HTML and CSS, I highly recommend the w3schools website.