Introduction to text editors in general
Not a word processor
A text editor must be differentiated from word processors.
An example of a word processor is LibreOffice Writer, which is released as Free and open-source software.
A word processor permits to create different kinds of documents (reports, letters, books, etc), with the ability to insert images, tables and other elements.
A text editor like gedit is used for creating and editing text files. The files that are saved by gedit and stored on disk contain only text.
Text file formats
With a text editor, you can write simple notes as free-form text. But the text can also follow a certain format.
Other programs take text files as input, read the text in it, and produce a result. For example, web browsers can read text files that follow the HTML format and renders them as pages.
A text file format specifies how the content needs to be structured in order to be understood by the other programs.
It is interesting to note that, with a simple text editor and text files, it is possible to write documents such as produced by a word processor.
To take our earlier example with HTML, to insert an image, it is done by referring to an external image file (for example stored on disk in the same directory). Although the image file is not part of the HTML file, a web browser knows that it needs to embed it in the page.
Text files are not restricted to write notes or documents, another area is writing source code, to develop a piece of software with a programming or scripting language.
When writing text in a certain format (or “language”), it is very useful to visually distinguish the different kinds of elements, when a portion of text has a special meaning. The special meanings depend on the syntax of the language, i.e., how things should be structured.
This is done by adding colors to the text (or other highlighting means: bold, italic, underline, etc).
It is important to note that these colors are not saved into the file; instead, it is the text editor application that presents the text to the user that way.