Introduction to indicators. Braille indicators are special-purpose characters including composition or markup indicators, change-of-semantics indicators, termination indicators and contraction indicators. The first three types of indicators are related: the first two affect the appearance and/or semantics of one or more affected cells while the third terminates such an effect.

Indicators are necessary to accomodate two aspects of braille: its small number of different characters and its standard linear presentation with all cells on the same baseline.

Composition or markup indicators. Braille uses embedded composition or printer's marks as markup symbols to indicate typesetting in a similar manner to HyperText Markup Language (HTML) and other modern markup languages. Examples are indicators for capitalization and for italics (or underlining).

Composition indicators precede the affected text. Braille composition indicators, in contrast to those of markup languages, remain embedded in braille texts and are intended to be read by braille readers. This requires their syntax to be much terser (more succint) than those of indicators—such as HTML tags—primarily intended to be read by a computer.

HTML uses explicit tags to indicate where an effect starts and also where it ends. For example, to indicate an italicized word in HTML you would precede it with <em> and follow it with </em>, for a total of nine additional symbols. Braille, by contrast, uses fewer characters for its indicators and has built-in defaults for their scope. The single-cell italics sign, for example, affects the following word by default. Only those cases not in accord with the defaults require a termination indicator to indicate the end of the markup. More complex cases like lists of titles also have special formatting rules.

Nemeth makes a greater use of markup than standard literary braille in order to indicate the nonlinear presentation of print mathematics. There are, for example, indicators for superscripts, subscripts, various types of fractions, and modifiers such as bars and arrows that appearly directly over or directly under a print character.

What is a change-of-semantics indicator? Since the braille alphabet only has a limited number of characters, braille uses special change-of-semantics indicators—analogous to the Shift or Alt keys on a computer keyboard—to indicate when certain cells are to be considered as corresponding to a different set of symbols. The number sign of literary braille and the Numeric and Punctuation Indicators in Nemeth are all change-of-semantics indicators.

Another important indicator in this category is the so-called English-Letter Indicator in Nemeth, which is dots 5-6. This is the same cell that is the letter sign in literary braille. In literary braille this cell is used to terminate the effect of the number sign before its default termination. In Nemeth this sign is used to indicate that a cell or cell sequence is "nothing more"; that is, it is one or more letters in their own right being used as a mathematical symbol and not as a contraction, acronym, or abbreviation. (An introduction to the need for this indicator is given on the page about transcribing.)

Neither the literary braille code nor the Nemeth code reserves a special set of cells to be used only for numerals.

In the literary code, numerals are represented using the same cells as are used for the letters a-j. Numerical useage is indicated by preceding the first digit of a number with dots 3-4-5-6 or the number sign, usually represented in print by the crosshatch mark, "#", also called the pound sign or number sign. The default termination of a number sign is a space and certain punctuation marks other than a comma.

The Nemeth code uses dots 3-4-5-6 for a similar purpose although it is usually called the Numeric Indicator rather than the number sign. Nemeth uses the lower-cell signs for the numbers rather than the corresponding upper-cell signs used in literary braille.

Nemeth makes a greater use of semantics indicators than standard literary braille. There are, for example, indicators for using the German, Greek, Hebrew, and Russian alphabets.

What is a termination indicator? A termination indicator is a braille symbol (usually one or two cells) that terminates the effect of a previous indicator. Termination indicators are sometimes used to end the effect of an indicator prior to its default termination point. (Change-of-semantic indicators also sometimes play this role.)

Termination indicators are also used rather like a "close parenthesis" to indicate the end of an effect which has an indefinite scope. In the Nemeth code, for example, the first character of a superscripted expression is preceded by a superscript composition indicator. The superscripted expression is terminated by the (return to) baseline indicator; the same indicator is also used to terminate general subscripted expressions. (Note that, by convention, purely numerical simple subscripts, but not superscripts, don't require this pair of indicators. This convention makes it easier to transcribe chemical formulas.)

Contraction indicators. A contraction indicator or general contraction indicator is a special cell used as a signal to indicate that the following cell is shorthand for a particular word or part-word.

What is an initial-letter contraction indicator? The three indicators with dot pattern 5 or NUMBRL code 02, dot pattern 4-5 or NUMBRL code 03, and dot pattern 4-5-6 or NUMBRL code 07 when used to precede a single-letter indicate that the letter is shorthand for a common letter sequence that starts with that letter. Initial-letter contractions can be used as either full words or part-words.

What is a final-letter contraction indicator? The three indicators with dot pattern 4-6 or NUMBRL code 05, dot pattern 5-6 or NUMBRL code 06, and dot pattern 6 or NUMBRL code 04 when used to precede a single-letter indicate that the letter is shorthand for a part-word letter sequence that ends with that letter.

This page was last modified January 10, 2002.