A document is composed of one or several blocks. A block correspond roughly to a html page, but it is also possible to insert one or more blocks into another.

Each block must have a name (a unique word) and a title. The entry point of the document is a block under the name main. It is this block which leads the readers to the entire content of the document.

### Creation of a block

To create a new block (except the entrance block main), you should first cite it in an existing block. When you read the latter, the citation becomes a link that leads you to the creation of the new block.

There are three wayt for a block to cite another one.

1. By a link. \link{link,The syntax of link} is very simple: it is enough to give the name of the cited block. One may also use links to cite blocks of other documents.
2. As a foldable part of the citing block. This part may be folded in and out as the readers wish. \link{fold,The syntax}.
3. As a transparently inserted part of the citing block. \link{embed, The syntax}.

### Fields "previous", "next" and "parent" of a block

The name of a block af the document has to be written in the fields "previous", "next" and "parent" of each block. These fields are used to

define the structure of the document.
- provide a reading order of all pages of the document (for instance, the reader could use the arrow Next to go to the next block of the block where it is; he could used the arrow Sup to go back to the parent block of the block he reads) ;
- define the blocks that appear in the printable version of the document: blocks appear in the printable version if and only if there is a link to them in their parent block and they appear in the link order (printable version is useful for example to search a word in a document).