A typical web page has a header and footer area. These two sections are crucial because they hold key info about your website. Ordinarily, most visitors to a website will notice the header first before anything else and they can make judgments about the website based on their impression of the header. Needless to say, the header and footer sections deserve more attention when designing your pages.
WordPress uses a simple templating system where all header content is contained in a piece of code stored in the header.php template file. Likewise, footer content is stored in the footer.php file. The code in these files is mostly plain HTML with bits of PHP code (template tags) that display the metadata dynamically.
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