HTML is a mark up language, which means that its use is to give the webpage its structure. For example, HTML is good for defining which text is the header and which is part of the paragraph. HTML provides little security, in terms of source code, and interactivity, in terms of getting feedback and showing motion. Flash, on the other hand, provides a graphic and motion orientated web interface. I think Flash is best when used for spontaneous and graphical motions on a webpage. In this case, both the action scripts and timelines of the animations are hidden from the view of the users. However, Flash provides no information for search engines, so this is where HTML can be used together with Flash. PHP and other dynamically-generated page technology are now more preferred in writing webpage, because first of all the source codes are hidden away from the viewers, which provide much more security. Although PHP and the like provide dynamic web contents, they are used mainly for server side applications, therefore, they do not entirely rule out the use of HTML.