I am a big fan of Programmer’s Notepad (PN) software. The developer of PN, Simon Steele, is working hard on releasing new versions. It can be pretty difficult nowadays to choose a notepad with text markup options since there are dozens of them available, both freeware and for purchase. I guess it is more a matter of taste and habit: once one has used a certain notepad for a while, its interface seems to be so logical and intuitive that using another notepad could be an irritating experience.
I have used PN for many years when working with HTML and CSS files. Of course, one can use Microsoft Visual Studio, but it is like using a sledgehammer to drive a nail. PN does not need to be installed on computers; it is, basically, just an executable file with a couple of libraries. It is very light and the performance of the search is relatively high as well. There are numerous rich functions, which are included in most typical word processing software; it provides a powerful and robust platform for tag-based editing as well as advanced text files editing. Although PN is freeware, you might consider donating to the project.