A CHM editor is designed to make editing CHM files easier. Instead of dealing with advanced programming skills, wading through pages of code, and downloading specific tools for working with CHM files, a CHM editor presents everything in a user-friendly program where the user can simply click through menus to make changes or translate a CHM file. This type of editor is known as a WYSIWYG editor, which stands for "What You See Is What You Get." This means the picture the user sees and edits on screen is what the document will actually look like. Other editors may show only the program's code and the user would have to save and preview the file to know what his changes would look like.
The CHM file is used with Microsoft® Compiled HTML Help. This program, first released as HTML Help 1.0, is owned by Microsoft® and used on all computers with a Windows® operating system. It is used primarily for creating online help documents which are composed largely of text instructions, a thorough index, hyperlinks, and a table of contents. Images may be used, but no fancy backgrounds or special formatting is applied. Computer users may be familiar with this format if they have ever opened a separate help screen with a search box at the top.
Microsoft® updated HTML Help up through version 1.33 after which it announced it would no longer update the program and would instead switch to a new program called Microsoft® Assistance Markup Language. HTML Help provided several advantages for those using it to create help programs and indexes. It created smaller files that could use international characters and provided one large index that could combine the indexes from several CHM files. These advantages made it much easier to use for writing help programs when compared to using traditional HTML.
Due to the difficulty of editing CHM files, the CHM editor grew in popularity. It allowed the user to open any CHM file and make changes to it, whether the user simply wanted to change the language or needed to make drastic changes to the contents of the file. CHM files were also used in certain types of electronic books, known as e-books, and anyone with these e-books could use a CHM editor on the file. Since HTML Help is used on any machine running Windows 98® or later, compatibility is not an issue and a user can open and edit a CHM file with a CHM editor from any computer with Microsoft®.