<\body> Besides sequences of instructions, which can be achieved using the primitive, and the mechanism of macro expansion, the style-sheet language provides a few other primitive for affecting the control flow: , , and . These primitives are available from the menu. However, we have to warn the user that the conditional constructs are quite fragile: they only apply to inline content and the accessibility of macro arguments should not to much depend on the conditions. The most important primitive , which can be entered using , allows for basic conditional typesetting: <\tm-fragment> ||>||>> >> In this example, is a block environment consisting of a title and a body, and which is rendered as a chapter for long documents and as a section for short ones. Notice that the following implementation would have been incorrect, since the primitive currently only works for inline content: <\tm-fragment> ||>||>>> >> The primitive may also be used in order to implement optional arguments: <\tm-fragment> |>|Hey , you look lonely today...|Hey and , you form a nice couple!>>>>> However, is not clever enough to detect which arguments are optional and which arguments are accessible ( which arguments can be edited by the user). Therefore, you will have to manually give this information using the primitive. The , and primitives are explained in more detail in the on the primitives|../../format/primitives/primitives.en.tm>. <\initial> <\collection>