standards are the technical specifications and guidelines to ensure that everyone has access to the content. Improved accessibility means more people can see it, in more browsers, on more devices. Complying to the standards ensures interoperability with browsers and forward compatibility.
standards allow us to strategically separate web pages into 3 components: structure, presentation and behavior. By effectively separating the content and the presentation you can best manage the site through a flexible and modular implementation.
modular code has functions which are elegant blocks of code that are reusable. So rather than writing large amounts of code over and over, you simply create a function and use it where it is needed. By editing one of these independent submodules, we can easily update the entire site since the submodule affects the modules that make up the site.