ttoreg.htm

TrueType字库标准文档

<FONT SIZE=2>A feature definition may not provide all the information
required to properly implement glyph substitution or positioning
actions. In many cases, a text-processing client may need to supply
additional data. For example, the function of the &quot;init&quot;
feature is to provide initial glyph forms. Nothing in the feature's
lookup tables indicates when or where to apply this feature during
text processing. To correctly use the &quot;init&quot; feature
in Arabic text where initial glyph forms appear at the beginning
of words, text-processing clients must be able to identify the
first glyph position in each word before making the glyph substitution.
In all cases, the text-processing client is responsible for applying,
combining, and arbitrating among features and rendering the result.
</FONT>
<P>
<FONT SIZE=2>The tag space defined by tags consisting of four
uppercase letters (A-Z) with no punctuation, spaces, or numbers,
is reserved as a vendor space. Font vendors may use such tags
to identify private features. For example, the feature tag &quot;PKRN&quot;
might designate a private feature that may be used to kern punctuation
marks. Microsoft does not guarantee the compatibility or usability
of private features, and it cannot ensure that two font vendors
will not choose the same tag for a private feature. Microsoft
does guarantee that it will not register or publish definitions
or tags of private features.</FONT>
<H3>To Register Features</H3>

<P>
<FONT SIZE=2>Microsoft encourages font developers to use registered
feature tags when implementing registered features. However, font
developers also may define and register their own features.</FONT>
<P>
<FONT SIZE=2>Microsoft welcomes nominations for new features and
feature tags to register. To qualify for registration, a feature
must have a single function that is clearly identified by its
tag. The function of the feature should be defined at the lowest
useful level and must be distinctly different from the functions
of currently registered features. When font developers register
feature tags and functions with Microsoft, they do not have to
supply implementation details.</FONT>
<P>
<FONT SIZE=2>Microsoft reserves the right to officially assign
feature tags in the Microsoft Tag Registry. Although Microsoft
has reserved the feature and feature tag definitions listed here,
Microsoft fonts do not contain all of the features.</FONT>
<H3>Registered Features</H3>

<P>
<I><B><FONT SIZE=2>Tag:    </FONT></B></I><B><FONT SIZE=2> &quot;init&quot;
<BR>
<I><B>Function:   </B></I></FONT></B><FONT SIZE=2>Provides initial
glyph forms</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation:<BR>
</FONT></B></I><FONT SIZE=2>In Microsoft's Arabic fonts, the &quot;init&quot;
feature replaces a default glyph located at the start of a word
with an initial form of the glyph. Microsoft implements the feature
as a single substitution lookup (GSUB LookupType = 1) for the
Arabic script.</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;medi&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides medial
glyph forms</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>In Microsoft's Arabic fonts, the &quot;medi&quot;
feature replaces a default glyph located in the middle of a word
with a medial glyph form of the glyph. Microsoft implements the
feature as a single substitution lookup (GSUB LookupType = 1)
for the Arabic script.</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;fina&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides final
glyph forms</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>In Microsoft's Arabic fonts, the &quot;fina&quot;
feature replaces a default glyph located at the end of a word
with a final form of the glyph. Microsoft implements the feature
as a single substitution lookup (GSUB LookupType = 1) for the
Arabic script. </FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;liga&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides ligature
glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;liga&quot; feature replaces
a string of glyphs with a ligature glyph. Microsoft defines this
feature with a ligature substitution lookup (GSUB LookupType =
4). The &quot;liga&quot; feature also might be implemented as
a contextual substitution that replaces a sequence of glyph classes
or coverage tables with a ligature glyph.</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;vert&quot;
 <BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Substitutes vertical
glyph variants for vertical text layout</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;vert&quot; feature replaces
default glyphs with vertically oriented glyph forms. Microsoft
implements this feature as a single substitution lookup (GSUB
LookupType = 1).</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;mark&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Positions mark
glyphs with respect to base glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;mark&quot; feature positions
mark glyphs in relation to a base glyph, a ligature glyph, or
another mark glyph. Microsoft implements this feature as a MarkToBase
Attachment lookup (GPOS LookupType = 4), MarkToLigature Attachment
lookup (GPOS LookupType = 5), or MarkToMark Attachment lookup
(GPOS LookupType = 6).</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;mset&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Positions Arabic
combining marks in fonts for Windows 95 using glyph  substitution</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>In contrast to the &quot;mark&quot;
feature, &quot;mset&quot; uses glyph substitution to combine marks
and base glyphs. It replaces a default mark glyph with a correctly
positioned mark glyph. The font designer specifies the position
of the mark when describing the mark's contour in the font file.
Microsoft's Arabic fonts, created for Windows 95, use a contextual
substitution lookup (GSUB LookupType = 5) to implement the &quot;mset&quot;
feature.</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;smcp&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides small
capital/uppercase glyphs, commonly called &quot;small caps&quot;</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;smcp&quot; feature replaces
lowercase glyphs with small uppercase glyphs. Microsoft implements
this feature with a single substitution lookup (GSUB LookupType
= 1).</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;onum&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides old
style numerals</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;onum&quot; feature replaces
default numeral glyphs with glyphs of old style numerals. Microsoft
implements the feature as a single substitution lookup (GSUB LookupType
= 1).</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;swsh&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides swash
glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation: <BR>
</FONT></B></I><FONT SIZE=2>The &quot;swsh&quot; feature replaces
default glyphs with swash versions of the glyph. Microsoft implements
the feature as an alternate substitution lookup (GSUB LookupType
= 3).</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;sups&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides superscript
glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;sups&quot; feature may replace
a default glyph with a superscript glyph, or it may combine a
glyph substitution with positioning adjustments for proper placement.
First, a single or contextual substitution lookup implements the
superscript glyph. Then, if the glyph needs repositioning, Microsoft
applies a single adjustment, pair adjustment, or contextual adjustment
positioning lookup.</FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;subs&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Provides subscript
glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;subs&quot; feature may replace
a default glyph with a subscript glyph, or it may combine a glyph
substitution with positioning adjustments for proper placement.
First, a single or contextual substitution lookup implements the
subscript glyph. . Then, if the glyph needs repositioning, Microsoft
applies a single adjustment, pair adjustment, or contextual adjustment
positioning lookup may then modify its position. </FONT>
<P>
<I><B><FONT SIZE=2>Tag:   </FONT></B></I><B><FONT SIZE=2> &quot;kern&quot;
<BR>
<I><B>Function:  </B></I></FONT></B><FONT SIZE=2>Adjusts amount
of space between glyphs</FONT>
<P>
<I><B><FONT SIZE=2>Microsoft Implementation<BR>
</FONT></B></I><FONT SIZE=2>The &quot;kern&quot; feature loosens
or tightens glyph spacing. Microsoft implements a pair positioning
lookup (GPOS LookupType = 2) when two glyphs are adjusted in relation
to another or a contextual positioning lookup in GPOS when more
than two glyphs are adjusted.</FONT>
<P>
<FONT SIZE=2>The TrueType Open &quot;kern&quot; feature is capable
of providing more information than a TrueType 1.0 &quot;kern&quot;
table. For instance, it supplies size dependent kerning data via
device tables, &quot;cross stream&quot; kerning in the Y text
direction, and independent adjustment of glyph placement and advance.</FONT>
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