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What a search engine sees when it loads one of your pages is not the same as what your browser sees. To understand why, you need to know how a Web page is created. Here's a quick explanation:
1. A user types a URL into his browser, or clicks a link, causing the browser to send a message to the Web server asking for a particular page.
2. The Web server grabs the page and quickly reads it to see if it needs to do anything to the page before sending it.
3. The Web server compiles the page, if necessary.
In some cases, the Web server may have to run ASP or PHP scripts, for instance, or it may have to find an SSI (server side include), an instruction telling it to grab something from another page and insert it into the one it's about to send.
4. After the server has completed any instructions, it sends the page to the browser.
5. When the browser receives the page, it reads through the page looking for instructions and, if necessary, further compiles the page.
6. When it's finished, the browser displays the page for the user to read.
Here are a few examples of instructions the browser may receive:
• It may find a <SCRIPT> tag, telling it to load a JavaScript from another file — it must then request this file from the server.
• It may find JavaScripts embedded into the file, in which case it runs those scripts.
• It may find references to images or other forms of media, and have to pull those into the page and read CSS (Cascading Style Sheets) instructions to see how the text should be formatted.
So, that's what happens normally when Web pages are created. But the searchbots, used by the search engines to index pages, work differently. When they request a page, the server does what it normally does, constructing the page according to instructions, and sends it to the searchbot. But the searchbot doesn't follow all the instructions in the page — it just reads the page. So, for example, it doesn't run scripts in the page.
 | ASP and PHP scripts are little programs that are written into Web pages. The scripts are read by a program working in association with the Web server when a page is requested. The searchbots see the results of the scripts because the scripts have been run by the time the Web server sends the page. Server side includes (SSIs) are simple statements placed into the HTML pages that name another file and, in effect, say to the Web server, "Grab the information in this file and drop it into the Web page here." Again, the searchbots see the information in the SSI because the Web server inserts the information before sending the Web page. |
You can add instructions that build the page in two ways:
- Browser-side (or client-side, but that strikes me as a very geeky term) instructions: Browser-side instructions are generally ignored by searchbots. For instance, if you create a page with a navigation system that is built with JavaScript, the search engines won't see it. Some people can even use browser-side instructions to intentionally hide things from the search engines.
- Server-side instructions: If you use an SSI to place navigation into the site, the searchbots will see it because the Web server uses the SSI before sending the information to the searchbots.
| Of course, it's possible for an SSI to place browser-side instructions into a page. In this case, the searchbot sees the instructions — because the server has placed them there — but will ignore them. |
This is a very important concept. Remember:
- Server-side = visible to searchbots
- Browser-side = not visible to searchbots
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