The use of HTML editors often causes problems. The safest way to make a document accessible is certainly to type directly in HTML. However, some other tools can also be used.
Tools to rule out are those which destroy all your adaptations for accessibility at each saving, and which rewrite on their own way all HTML elements. Tools that do not allow the HTML code to be directly edited should also be avoided. In fact, these are all the tools that do not permit you any control on the HTML code you are writing. In such cases, it is necessary to use a word processing program to correct the code (this stage is boring since this code is automatically generated without any control and it is rarely clear !).