Omission of articles

Could you please explain, if possible, according to what principles articles tend to be omitted in English? There are related textbook rules regarding proper names, uncountable nouns, headings/titles, however, this is not what I'm concerned about. I tend to notice on a daily basis here and there that articles are omitted from where they must be used according to rules, and I don't notice any pattern according to which they are omitted. Unfortunately, I can't provide lots of examples, however, I can provide at least one. In here, https://css-tricks.com/snippets/jquery/move-cursor-to-end-of-textarea-or-input/, it's not 'the end of a textarea', it's just 'end'. Even though it is a title, I frequently notice very similar omissions in the middle of texts of different styles and genres, however I do not understand what the pattern of this omission could be. If what I'm trying to ask makes sense, could you please tell me how that omission works in English?