The first thing we need to do is to make sure we are looking at te source of the web page as displayed by a web browser. This will make sure that none of what we are looking at is code written in a server side language that is being used to generate the web page If you need to determine what's what in the original source then comparing the original file with the page the way it appears in a web browser will identify for you all those sections of the code that represent server side processing.
One thing to watch out for when viewing the source of the page in a web browser is that the source you see is the way the web browser is interpreting it. With some web browsers such as Internet Explorer the source will have been converted slightly to match the way the browser expects to process it. You may want to compare the source of a web page in several different browsers so that you can tell what may be due to changes made by a particular browser.