Paragraph layout (FSF GNU project)

Paragraph layout

par-mode≔justify

(paragraph alignment)

This environment variable specifies the alignment of the different lines in a paragraph. Possible values are left, center, right and justify:

This paragraph is aligned to the left. This paragraph is aligned to the left. This paragraph is aligned to the left.	This paragraph is has been centered. This paragraph is has been centered. This paragraph is has been centered.
This paragraph is aligned to the right. This paragraph is aligned to the right. This paragraph is aligned to the right.	This paragraph has been justified. Justification is the default alignment mode for paragraphs. So be it.

Table 1. The supported modes for alignment.

par-hyphen≔normal

(quality of hyphenation)

This parameter controls the quality of the hyphenation algorithm. Possible values are normal and professional. The professional hyphenation algorithm uses a global algorithm on the entire paragraph, whereas the normal one uses a faster first-fit algorithm.

The difference between the different hyphenation algorithms provided by TeXmacs is seen best for long paragraphs which are typeset into a narrow column. The professional hyphenation usually succeeds to minimize the number of ugly gaps between words.

Table 2. Comparison different hyphenation algorithms. At the left hand side, we have used the normal algorithm and on the right hand side the professional one. Even though there are some ugly gaps at the right hand side around “hyphenation”, the really bad gap around “The” on the left hand side has been avoided.

par-width≔auto

(paragraph with)

This environment variable controls the width of paragraphs. By default, it is automatically determined as a function of the page (or screen) size and margins.

par-left≔0cm

par-right≔0cm

(left and right margins)

These environment variables specify absolute left and right margins for the paragraph, with respect to the default left and right margins (which are determined as a function of the page layout). For instance:

This text uses the default margins.

This text uses a left margin of 1cm

This text uses a left margin of 2cm

This text uses a left margin of 3cm

The left and right margins of this text have both been set to 3cm.

Environments like itemize and quote-env which maybe nested usually compute new margins as a function of the old values by adding or subtracting some space:

< assign | quote-env | < macro | body |

<\surround|

<vspace*|0.5fn>

<right-flush><vspace|0.5fn>

> >

par-first≔1.5fn

(first indentation)

The par-first parameter specifies the additional indentation which is used for the first line of the paragraph. The aim of first indentations is to indicate the starts of new paragraphs. An alternative technique is the use of vertical whitespace.

The article and book styles in TeXmacs indictate the starts of new paragraphs through the use of a first indentation.

The generic and letter styles rather use vertical whitespace.

The generic and letter styles in TeXmacs indictate the starts of new paragraphs through the use of vertical whitespace.

The article and book styles rather use a first indentation.

Table 3. Two classical ways to indicate the starts of new paragraphs.

par-sep≔0.2fn

(extra separation between successive lines)

The sum of the font size and par-sep determines the ideal distance between two successive base lines in a paragraph (also called the “base line skip”). Of course, when the lines contain large boxes, then this distance may need to be increased. When 1fn for par-sep, one may for instance produce documents with a double interline space:

A double interline space corresponds to par-sep≔1fn. Double interline spaces are often used by lazy people who want to pretend that they have written many pages. They generally do not care about tropical rain forests.

In the case when two successive lines use different base line skips, then the maximal value is used in order to compute the ideal distance between their baselines. This allows for a reasonable spacing when the font size is changed from one paragraph to another:

Normal text.

Some very large text.

And back to normal.

par-line-sep≔0.025fn*

(extra space between lines)

This parameter corresponds an additional stretchable amount of whitespace between successive lines in a paragraph. Setting par-line-sep to a small stretchable value which defaults to 0 allows the page breaker to correctly stretch pages which contain a very long textual paragraph. Indeed, par-line-sep vanishes, then the height of a textual paragraph is of the form a + b n, where a and b are constants and n is the number of lines. There is no reason why the usable height of a page should be of this form.

par-par-sep≔0.5fn*

(extra space between paragraphs)

The par-par-sep parameter specifies the amount of vertical whitespace which separates two successive paragraphs. This space is determined in stretchable length units. By default, TeXmacs does not use any whitespace between successive paragraphs, except when no nice page breaks could be found (this explains the use of the fn* length unit). Starts of new paragraphs are rather indicated through the use of first indentations (see table ?).

In the case when two successive paragraph use different paragraph separations, then the maximum of the two is taken. In fact, the par-par-sep length is added to both the vertical spacing before and the vertical spacing after the paragraph.

par-hor-sep≔0.5fn

par-ver-sep≔0.2fn

(minimal space between ink)

When a paragraph contains several exceptionally large boxes, then TeXmacs attempts to “shove successive lines into another” as long as none of the boxes collide:

Consider a fraction which decends more than usual like

x + 1

at the end of a line and an expression like ⅇ ^{ⅇ^x} which is higher than usual.

When these expressions occur at different places, then TeXmacs tries to render the successive lines in a compact manner.

In the case of a fraction

x + 1

and an exceptionally high expression at the wrong place, like the expression ⅇ ^{ⅇ^x} here, the boxes are separated by env-ver-sep .

As soon as the horizontal distance between two large boxes is less than par-hor-sep, then they are considered to be in collision. In that case, the vertical distance between them must be at least par-ver-sep. Also, the amount of showing never exceeds 1ex.

When using an interline space of 1.5 or 2, the default value of par-ver-sep allows the user to type larger formulas in the text while preserving a uniform layout. When using a small par-sep and a large par-ver-sep, the distance between two successive lines remains small, except when their contents are horizontally close. This may for instance be used to reduce the space between a short like followed by a centered equation.

par-fnote-sep≔0.2fn

(minimal space between different footnotes)

This parameter controls the amount of vertical space between successive footnotes.

par-columns≔1

(number of columns)

This environment variable specifies the number of columns into which the text is being typeset. Different numbers of columns may be used successively in the same document.

par-columns-sep≔2fn

(distance between columns)

This environment variable specifies the amount of horizontal whitespace which separates different columns in multi-column mode.

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