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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="unicode-character-categories"></a>Unicode character categories</h2></div></div></div>
<p>
Shaping models are typically specified with respect to how
scripts are defined in the Unicode standard.
</p>
<p>
Every codepoint in the Unicode Character Database (UCD) is
assigned a <span class="emphasis"><em>Unicode General Category</em></span> (UGC),
which provides the most fundamental information about the
codepoint: whether the codepoint represents a
<span class="emphasis"><em>Letter</em></span>, a <span class="emphasis"><em>Mark</em></span>, a
<span class="emphasis"><em>Number</em></span>, <span class="emphasis"><em>Punctuation</em></span>, a
<span class="emphasis"><em>Symbol</em></span>, a <span class="emphasis"><em>Separator</em></span>,
or something else (<span class="emphasis"><em>Other</em></span>).
</p>
<p>
These UGC properties are "Major" categories. Each codepoint is
further assigned to a "minor" category within its Major
category, such as "Letter, uppercase" (<code class="literal">Lu</code>) or
"Letter, modifier" (<code class="literal">Lm</code>).
</p>
<p>
Shaping models are concerned primarily with Letter and Mark
codepoints. The minor categories of Mark codepoints are
particularly important for shaping. Marks can be nonspacing
(<code class="literal">Mn</code>), spacing combining
(<code class="literal">Mc</code>), or enclosing (<code class="literal">Me</code>).
</p>
<p>
In addition to the UGC property, codepoints in the Indic and
Southeast Asian scripts are also assigned
<span class="emphasis"><em>Unicode Indic Syllabic Category</em></span> (UISC) and
<span class="emphasis"><em>Unicode Indic Positional Category</em></span> (UIPC)
properties that provide more detailed information needed for
shaping.
</p>
<p>
The UISC property sub-categorizes Letters and Marks according to
common script-shaping behaviors. For example, UISC distinguishes
between consonant letters, vowel letters, and vowel marks. The
UIPC property sub-categorizes Mark codepoints by the relative visual
position that they occupy (above, below, right, left, or in
multiple positions).
</p>
<p>
Some complex scripts require that the text run be split into
syllables. What constitutes a valid syllable in these
scripts is specified in regular expressions, formed from the
Letter and Mark codepoints, that take the UISC and UIPC
properties into account.
</p>
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