<\body> <\explain|>|par-n>> This primitive is used for sequences of logical paragraphs. A simple, plain text document is made of a sequence of paragraphs. For instance, <\tm-fragment> A simple document. Made of several paragraphs. The second paragraph is very long, so that it is hyphenated across several line. is internally represented as a with two subtrees: <\tm-fragment> A simple document. Made of several paragraphs. The second paragraph is very long, so that it is hyphenated across several line. > From the visual point of view, different paragraphs are often separated by some vertical whitespace. Alternatively, new paragraphs are indicated through the use of an additional indentation. The root of a document is usually a node. The tag is also used for marking multi-paragraph content inside other tags, such lists or theorem-like environments. Environments which require the use of a tag for at least one argument are called ``block environments''. <\explain|>|unit-n>> This not yet implemented primitive is a variant of . While a document is made up of logical paragraphs, a paragraph is made up of ``paragraph units''. From a visual point of view, different paragraphs are singled out using some additional space or indentation. New paragraph units rather correspond to simple new lines. Typically, displayed equations are also paragraph units in a larger paragraph. <\explain|>|item-n>> This primitive is used for sequences of line items, also called ``inline content''. For instance, <\tm-fragment> Some text. is internally represented as: <\tm-fragment> text.>> The operator is essential to put compound structures in trees taking multiple parameters. For example, let us place the previous fragment in a multi-paragraph context: <\tm-fragment> Multiple paragraphs. Some text. In this example, we need the tag in order to indicate that ``Some text.'' correponds to a single paragraph: <\tm-fragment> A simple document. Some text. > Notice that block tags like may contain inline tags such as as its children, but not . In order to typeset line content before or after block content, one has to use the tag below. <\explain> <|explain> Although it is not possible in to use block content inside horizontal concatenations, it is sometimes useful to add some additional inline content before or after a block environment. The primitive serves this purpose, by adding a and surrounding to some block content . For instance, <\tm-fragment> <\inactive*> <\surround|>> >|> <\theorem> \{F}> and g\\> with 0>, there exists an \> with .> produces <\tm-fragment> <\surround|>> |> <\theorem> Given \{F}> and g\\> with 0>, there exists an \> with . In general, the is mainly used in style files, but it occasionally turns out to be useful in regular documents as well. <\initial> <\collection>