<\body> lengths> A simple length is a number followed by a length unit, like or . supports three main types of units: <\description> The length of an absolute unit like or on print is fixed. Context-dependent length units depend on the current font or other environment variables. For instance, corresponds to the height of the ``x'' character in the current font and correspond to the current paragraph width. Any nullary macro, whose name contains only lower case roman letters followed by , and which returns a length, can be used as a unit itself. For instance, the following macro defines the length: <\tm-fragment> >> Furthermore, length units can be . A stretchable length is represented by a triple of rigid lengths: a minimal length, a default length and a maximal length. When justifying lines or pages, stretchable lengths are automatically sized so as to produce nicely looking layout. In the case of page breaking, the environment provides additional control over the stretchability of white space. When setting the to , stretchable spaces behave as usual. When setting the to , stretchable spaces become rigid. For other values, the behaviour is linear. <\description> >One centimeter. >One millimeter. >One inch. >The standard typographic point corresponds to of an inch. >A big point corresponds to of an inch. >The Didôt point equals 1/72 of a French inch, . >One ``pica'' equals 12 points. >One ``cicero'' equals 12 Didôt points. <\description> >The font size. When using a font, corresponds to . >The base font size. Typically, when selecting as the font size for your document and when typing large text, the base font size is and the font size . >The width of a nicely looking fraction bar for the current font. >A typical separation between text and graphics for the current font, so as to keep the text readable. For instance, the numerator in a fraction is shifted up by . >The height of the fraction bar for the current font (approximately ). >The height of the ``x'' character in the current font. >The width of the ``M'' character in the current font. <\description> >This is a stretchable variant of . The default length of is . When stretched, may be reduced to and extended to . >This length defaults to zero, but it may be stretched up till . >The ``base line skip'' is the sum of and . It corresponds to the distance between successive lines of normal text. Typically, the baselines of successive lines are separated by a distance of (in and a slightly larger space is used though so as to allow for subscripts and superscripts and avoid a too densely looking text. When stretched, may be reduced to and extended to . >The (stretchable) width of space character in the current font. >The additional (stretchable) width of a space character after a period. Box length units can only be used within some special markup elements, such as , , , and . The principal body of this content ( the content being ``moved'' in the case of ) is typeset as a box. The following lengths units then correspond to the size and the extents of the box. <\description> >The width of the box. >The height of the box. >The logical left -coordinate of the box. >The logical right -coordinate of the box. >The logical bottom -coordinate of the box. >The logical top -coordinate of the box. For instance, the code <\tm-fragment> >> can be used to center > at the base-line. <\description> >The width of the paragraph. That is the length the text can span. It is affected by paper size, margins, number of columns, column separation, cell width (if in a table), >The height of the main text in a page. In a similar way as , this length unit is affected by page size, margins, >One screen pixel, the meaning of this unit is affected by the shrinking factor. >The smallest length unit for internal length calculations by . divided by the shrinking factor corresponds to . There are three types of lengths in : <\description> A string consisting of a number followed by a length unit. An abstract length is a macro which evaluates to a length. Such lengths have the advantage that they may depend on the context. All lengths are ultimately converted into a normalized length, which is a tag of the form (for rigid lengths) or (for stretchable lengths). The user may also use this tag in order to specify stretchable lengths. For instance, |1quad|1.5quad>> evaluates to a length which is by default, at least and at most . <\initial> <\collection>