I need some thoughts on code duplication and separation

Hi. I am working on a small system where I am both trying to avoid code duplication and at the same time I am trying to keep the presentation logic separated from the application logic. I am using sessions and are avoiding "headers already sent" problem by keeping the HTML out of the application. For example, I would like to have a common header.php file, but it is difficult to create this since one file needs to have some specific Javascript located in the <head> </head> tags, but the other files doesn't need this. Another file needs to have a specific "onload" call in the <body> tag, while yet another file also needs to have an "onload" call, but with different attributes. I have been looking around in other systems to see what kinds of solutions are being used - as inspiration. I have been thinking about the following solutions: 1. Create only ONE header.php file that contains a lot of conditionals depending on what file is including it - the output of HTML/Javascript changes. I believe this would turn into a very ugly hack. Difficult to maintain. 2. Create a HTML generating class with a set of methods that each contains an adequate amount of parameters. Each method maintains its own HTML tag. For example, docType($type) would generate the doctype specification. I believe this is a "cleaner" solution, but the problem with code duplication isn't avoided. Some of the presentation logic contains conditionals and the HTML changes when the conditional changes, hence the header content changes, but the <doctype>, <html>, and <head> doesn't necessarily change and they would get duplicated a couple of times in some files. 3. Avoid the problem all together, use output buffering and completely forget about separation between application and presentation. I hope I make sense. Any thoughts on these kinds of problems? Best regards.