Glossary

advance height The distance from the top of a glyph to the bottom of the glyph, including the top-side bearing and bottom-side bearing.

advance width The full horizontal width of a glyph as measured from its origin to the origin of the next glyph on the line, including the side bearings on both sides.

alignment The process of placing text in relation to one or both margins.

alphabetic writing system The glyphs that symbolize discrete phonemic elements in a language. Compare syllabic writing system and ideographic writing system.

angled caret A caret whose angle in relation to the baseline of the display text is equivalent to the slant of the glyphs making up the text. Compare straight caret.

ascent line An imaginary horizontal line that corresponds approximately to the tops of the uppercase letters in the font. Uppercase letters are chosen because, among the regularly used glyphs in a font, these are generally the tallest.

automatic form substitution The process of automatically substituting one or more glyphs for one or more other glyphs.

baseline An imaginary line used to align glyphs in a line of text.

baseline delta An offset (in points) between the various baseline types and y = 0. See baseline type.

baseline type The classification of baseline used with a particular kind of text. See, for example, Roman baseline.

bidirectional script system A script system where text is generally right-aligned with most characters written from right to left, but with some left-to-right text as well. Arabic and Hebrew are bidirectional script systems.

bottom-side bearing The white space between the bottom of the glyph and the visible ending of the glyph.

bounding box The smallest rectangle that entirely encloses the pixels or outline of a glyph.

caret A vertical or slanted blinking bar, appearing at a caret position in the display text, that marks the point at which text is to be inserted or deleted. Compare split caret.

caret angle The angle of a caret or the edges of a highlight. The caret angle can be perpendicular to the baseline or parallel to the angle of the style run's text.

caret position A location on screen, typically between glyphs, that relates directly to the offset (in memory) of the current text insertion point in the source text. At the boundary between a right-to-left and left-to-right direction run on a line, one character offset may correspond to two caret positions, and one caret position may correspond to two offsets.

caret type A designation of the behavior of the caret at direction boundaries in text. See split caret.

character A symbol standing for a sound, syllable, or notion used in writing; one of the simple elements of a written language, for example, the lowercase letter "a" or the number "1". Compare character code, glyph.

character cluster A collection of characters treated as individual components of a whole, including a principal character plus attachments in memory. For example, in Hebrew, a cluster may be composed of a consonant, a vowel, a dot to soften the pronunciation of the consonant, and a cantillation mark.

character code In ATSUI, a 16-bit value representing a Unicode text character. Text is stored in memory as character codes. Each script system's keyboard-layout ('KCHR') resource converts the virtual key codes generated by the keyboard or keypad into character codes; each script system's fonts convert the character codes into glyphs for display or printing.

character encoding An internal conversion table for interpreting a specific character set.

character offset The indexed position of a 2-byte Unicode character in a text buffer, starting at zero for the first character. Sequential values for character offset correspond to the storage order of the characters. (2) The horizontal separation between a character rectangle and a font rectangle--that is, the position of a given character within the font's bit image.

contextual form An alternate form of a glyph whose use depends on the glyph's placement in a word.

counter The oval in glyphs such as "p" or "d".

cross-stream kerning The automatic movement of glyphs perpendicular to the line orientation of the text. Compare with-stream kerning.

cross-stream shift A type of positional shift that applies equally to all glyphs in a style run by raising or lowering the entire style run (or shifts it sideways if it's vertical text). Compare with-stream shift.

cursor A small icon, often an arrow or an I-beam shape, that moves with the mouse or other pointing device. Compare caret.

descent line An imaginary horizontal line that usually corresponds with the bottoms of the descenders in a font. The descent line is the same distance from the baseline for all glyphs in the font, whether or not they have descenders.

direction See dominant direction, glyph direction, line direction, text direction.

direction boundary A point between offsets in memory or glyphs in a display, at which the direction of stored or displayed text changes.

direction level A hierarchical ranking of dominant direction in a line. Direction levels can be nested so that complex mixed-direction formatting is preserved.

direction-level run A sequence of contiguous glyphs that share the same text direction.

direction override A means of overriding the directional behavior of glyphs, on a style-run basis, for special effects.

discontiguous highlighting Highlighting that exactly matches the selection range it corresponds to. It may consist of discontiguous areas when the selection range crosses direction boundaries. Compare contiguous highlighting.

display order The left-to-right order in which ATSUI displays glyphs. Display order determines the glyph index of each glyph in a line and may differ from the input order of the text. See glyph index; compare input order and source text.

display text The visual representation of the text of a text layout object. Display text consists of a sequence of glyphs, arranged in display order. Compare source text.

dominant direction The direction in which successive groups of glyphs are read. Dominant direction is independent of glyph direction. See also glyph direction, line direction.

drop capital A large uppercase letter that drops below the main line of text for aesthetic reasons.

dual caret See split caret.

dynamic highlighting The process of continually drawing and redrawing the highlighted area as the user moves the cursor through the text while holding down the mouse button.

edge offset A byte offset into the source text of a layout shape that specifies a position between byte values. Edge offsets in source text are related to caret positions in display text. Compare caret position and byte offset.

feature selectors A means of defining particular font features in a feature type. See also feature type.

feature type A group of font features in a style object that are applied to each style run based on font defaults. See also feature selectors.

font A collection of glyphs that usually have some element of design consistency such as the shapes of the counters, the design of the stem, stroke thickness, or the use of serifs.

font attributes A group of flags that modify the behavior or identity of a font.

font embedding The technique of storing a font object's binary data in a document so that the text in the document always displays the correct font.

font family A group of fonts that share certain characteristics and a common family name.

font features The set of typographic and layout capabilities that create a specific appearance for a layout shape.

font instance A setting identified by the font's designer that matches specific values along the available variation axes and gives those values a name.

font name A set of specific information in a font object about a font, such as its family name, style, copyright date, version, and manufacturer. Some font names are used to build menus in an application, whereas other names are used to identify the font uniquely.

font object An object type that hides the complexity of font data from your application.

font variation An algorithmic way to produce a range of typestyles along a particular variation axis.

font variation suite A complete listing of every axis supported in a font in the order specified by the font. Each axis is given a value in the listing.

glyph The distinct visual representation of a character in a form that a screen or printer can display. A glyph may represent one character (the lowercase a ), more than one character (the fi ligature), part of a character (the dot over an i ), or a nonprinting character (the space character). See also character.

glyph code A number that specifies a particular glyph in a font. Fonts map character codes to glyph codes using Unicode 'cmap' tables, which in turn specify individual glyphs. If a font does not have a Unicode 'cmap' table, it is generated automatically.

glyph direction The direction in which successive glyphs are read. Compare dominant direction.

glyph ductility The ability to stretch the actual form of a glyph during justification.

glyph index The order of a glyph in a line of display text. The leftmost glyph in a line of text has a glyph index of 1; each succeeding glyph to the right has an index one greater than the previous glyph. Compare glyph code, edge offset.

glyph origin The point that ATSUI uses to position a glyph when drawing.

grow limit The maximum amount by which glyphs of a given priority can be extended during justification, before processing passes to glyphs of lower priority. Compare shrink limit.

hanging baseline The baseline used by Devanagari and similar scripts, where most of the glyph is below the baseline.

hanging glyphs A set of glyphs, usually punctuation, that typically extend beyond the left and right margins of the text area and whose widths are not counted when line length is measured.

highlighting The display of text in inverse video or with a colored background. Highlighting in display text corresponds to a selection range in source text.

highlight type The angular character of carets and edges of highlighting areas. Highlighting and carets are either straight or angled; see angled caret, straight caret.

hit-testing The process of converting a location within a line of display text into a caret offset in the source text of that line.

ideographic centered baseline The baseline used by Chinese, Japanese, and Korean ideographic scripts, in which glyphs are centered halfway on the line height.

ideographic writing system The glyphs that symbolize component meanings of words in a language. Compare syllabic writing system and alphabetic writing system.

imposed width A run control feature that forces a specific width onto the glyphs of a style run, regardless of its text content or other style properties.

index See glyph index.

input order The order in which characters are written or entered from a keyboard. The input order of a line of text can differ from its display order. Compare display order.

insertion point The point in the source text at which text is to be inserted or deleted. An insertion point is specified by a single caret position. Compare caret; see also caret position.

justification The process of typographically expanding or compressing a line of text to fit a text width.

justification gap The difference in the length of a line before and after justification.

justification priority The priority order in which classes of glyphs are processed during justification.

kashida An extension-bar glyph that is added to certain Arabic glyphs during justification.

kerning An adjustment to the normal spacing that occurs between two or more specifically named glyphs, known as the kerning pair .

kerning adjustments array An array in the style object that overrides the normal kerning for individual pairs of glyphs by specifying a point-size factor and scaling factor.

kerning pair Two specifically named glyphs that are kerned together by a set amount. See also kerning.

language The written and spoken methods of combining words to create meaning used by a particular group of people.

leading edge The edge of a glyph that is encountered first when reading text of that glyph's language. For glyphs of left-to-right text, the leading edge is the left edge; for glyphs of right-to-left text, the leading edge is the right edge.

left-side bearing The white space between the glyph origin and the visible beginning of the glyph.

ligature Two or more glyphs connected to form a single new glyph.

ligature decomposition The replacement of ligatures with the glyphs for their component characters during justification.

ligature splitting The process of separating a ligature into its component glyphs.

line breaking The process of determining the proper location at which to truncate a line of text so that it fits within a given text width.

line direction The overall direction in which a line of text is read. Line direction is the lowest nested level of dominant direction on a line.

line length The distance, in points, from the origin of the first glyph on a line through the advance width of the last glyph.

line span The distance, in points, from the lowest descender on a line to the highest ascender.

margins The left, right, top, and bottom sides of the text area.

math baseline The baseline used for setting mathematical expressions; it is centered on operators such as the minus sign.

mixed-direction text The combination of text with both left-to-right and right-to-left directions within a single line of text.

neutral type A glyph directionality in which the glyph direction is always that of the surrounding glyphs. Compare strong type, weak type.

point size The size of a font's glyphs as measured from the baseline of one line of text to the baseline of the next line of single-spaced text. In the United States, point size is measured in typographic points.

postcompensation action The extra processing, such as addition of kashidas and ligature decomposition, that occurs after glyphs have been repositioned during justification.

priority justification override array An array that alters the standard justification behavior for all glyphs of a given justification priority.

right-side bearing The white space on the right side of the glyph; this value may or may not be equal to the value of the left-side bearing.

Roman baseline The baseline used in most Roman scripts and in Arabic and Hebrew.

run A sequence of glyphs that are contiguous in memory and share a set of common attributes.

script A method for depicting words visually.

selection range The contiguous sequence of characters in the source text that mark where the next editing operation is to occur. The glyphs corresponding to those characters are commonly highlighted on screen.

serif The fine lines stemming from and at an angle to the upper and lower ends of the main strokes of a letter--for example, the little "feet" on the bottom of the vertical strokes in the upper-case letter "M" in Times Roman typeface.

style run text attributes The set of flags that allow you to specify how ATSUI alters glyph outlines or chooses the proper metrics for horizontal or vertical text.

shrink limit The maximum amount by which glyphs of a given priority may be compressed during justification, before processing passes to glyphs of lower priority. Compare grow limit.

smart swash A variation of an existing glyph (often ornamental) that is contextual. Compare swash .

soft line break Line breaks within a text layout object.

source text A stored sequence of character codes that represents a line of text. Characters in source text are stored in input order. Compare display order, display text; see also input order.

split caret A type of caret that, at the boundary between text of opposite directions, divides into two parts: a high caret and a low caret, each measuring half the line's height. The two separate half-carets merge into one in unidirectional text.

storage order See input order, display order, source text.

straight caret A caret that is perpendicular to the baseline of the display text, regardless of the angle of the glyphs making up the text. Compare angled caret.

strong type A glyph directionality that is always left to right or right to left. Compare weak type, neutral type.

style run A sequence of memory backing store contiguous glyphs that share the same style.

swash A variation of an existing glyph (often ornamental) that is noncontextual. Compare smart swash.

syllabic writing system The glyphs that symbolize syllables in a language. Compare alphabetic writing system and ideographic writing system.

text A set of specific symbols that, when displayed in a meaningful order, conveys information.

text area The space on the display device within which the text should fit.

text direction The direction in which reading proceeds. Roman text has a left-to-right direction; Hebrew and Arabic have a (predominantly) right-to-left direction; Chinese and Japanese can have a vertical direction.

text run A complete unit of text, made up of character codes or glyph codes.

text width The area between the margins; it is the length available for displaying a line of text.

tiled highlighting A highlighting mechanism whereby the highlighted area corresponding to every character in a line of text is unique, without gaps or overlaps.

top-side bearing The white space between the top of the glyph and the visible beginning of the glyph.

tracking Kerning between all glyphs in the shape, not just the kerning pairs already defined by the font. You can increase or decrease interglyph spacing by using a track number. See kerning.

track setting A value that specifies the relative tightness or looseness of interglyph spacing.

trailing edge The edge of a glyph that is encountered last when reading text of that glyph's language. For glyphs of left-to-right text, the trailing edge is the right edge; for glyphs of right-to-left text, the trailing edge is the left edge.

typestyle A variant version of glyphs in the same font family. Typical typestyles available on the Macintosh computer include bold, italic, underline, outline, shadow, condensed, and extended.

typographic bounding rectangle The smallest rectangle that encloses the full span of the glyphs from the ascent line to the descent line.

typographic point A unit of measurement describing the size of glyphs in a font. There are 72.27 typographic points per inch, as opposed to 72 points per inch in ATSUI.

unidirectional text A sequence of text that has a single direction. Compare mixed-direction text.

unlimited gap absorption The assignment of all justification gap to an individual glyph or priority of glyphs, regardless of the specified grow or shrink limits for that glyph or glyphs.

variation axis A range included in a font by the font designer that allows a font to produce different typestyles.

weak type A glyph directionality that depends on context to determine whether it is left to right or right to left. Compare strong type, neutral type.

with-stream kerning The automatic movement of glyphs parallel to the line orientation of the text. Compare cross-stream kerning.

with-stream shift A positional shift that applies equally to all glyphs in a style run by adding or removing space before or after each glyph in the run. Compare cross-stream shift.

WorldScript A group of Macintosh system software managers, extensions, and resources that facilitate multilanguage text processing.

x-height The position where the top of the lowercase "x" in the font lies; this measurement usually marks the height of the body of all lowercase glyphs, excluding ascenders and descenders, in the font.