<\body> Usually, long documents have a structure: they are organized in chapters, sections and subsections, they contain different types of text, such as regular text, citations, footnotes, theorems, etc. After selecting a in , takes care of specific layout issues, such as numbering of sections, pages, theorems, typesetting citations and footnotes in a nice way and so on. Currently, several standard document styles have been implemented: , , , , , , , . For instance, the article style can be used for writing articles. Besides, there are styles for common journals and special purposes, such as the documentation. As soon as you have selected a document style, you can organize your text into sections (see ) and use specific (also called ). Examples of environments are theorem, proposition, remark and so on (see ). Other examples are lists of items (see ) or numbered lists (see ). Further examples of frequently used tags are (for writing ``important'' text), (for writing names of persons), etc. When you get more acquainted with , it is possible to add your own new environments in your own style file. Assume for instance that you often make citations and that you want those to appear in italic, with left and right margins of 1cm. Instead of manually changing the text and paragraph properties each time you make a citation, it is better to create a citation environment. Not only it will be faster to create a new citation when doing so, but it is also possible to systematically change the layout of your citations throughout the document just by changing the definition of the citation environment. The latter situation occurs for instance if you discover that you prefer the citations to appear in a smaller font. There are a few general editing principles which make it easy to manipulate structured documents using . One major concept is the , which is best illustrated on an example. Assume that we are in the process of entering a classical theorem: <\quote-env> The following theorem is due to : <\big-envbox> <\theorem> *\>=\1>>. At the position of the cursor, the grey and cyan boxes indicate the active tags: in this case, the cursor is both inside a theorem and a formula. The innermost active tag (the formula *\>=\1> in our example) is surrounded by a cyan box and called the . The contents of the menu and (the lowest toolbar) are highly context dependent and determined as a function of the current focus. In our example, the focus toolbar contains apopup menu button ; when selecting in this menu, the text will change into <\quote-env> The following theorem is due to : <\big-envbox> <\theorem> \; <\big-focus> <\equation*> \*\>=\1. Similarly, the arrow buttons on the left hand side of the focus toolbar allow you to jump to similar tags. In this case, they will allow you to quickly traverse all formulas and equations in your document. For more information on ``'' we refer to the chapter on . A second important concept is the . Currently, there are five major modes: text mode, mathematics mode, program mode, graphics mode and source mode. In principle, the current mode can be determined from the current focus, but the mode is likely to change less often than the focus. The above the focus toolbar contains several buttons which are useful in the current mode. The contents of the and menus are also mode dependent. <\initial> <\collection>