SILE is a typesetting system.
Its job is to produce beautiful printed documents.
The best way to understand what SILE is and what it does is to compare it to other systems which you may have heard of.
SILE versus Word
When most people produce printed documents using a computer, they usually use software such as Word (part of Microsoft Office) or Writer (part of Open/LibreOffice) or similar–word processing software.
SILE is not a word processor; it is a typesetting system.
There are several important differences.
The job of a word processor is to produce a document that looks exactly like what you type on the screen.
SILE takes what you type and considers it instructions for producing a document that looks as good as possible.
For instance, in a word processor, you keep typing and when you hit the right margin, your cursor will move to the next line.
It is showing you