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<a name="old-Contexts-explained"></a>
Up: <a rel="up" accesskey="u" href="Discussion-of-specific-tweaks.html#Discussion-of-specific-tweaks">Discussion of specific tweaks</a>
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<h4 class="subsection">5.7.1 old Contexts explained</h4>
<!-- FIXME Delete this section? It is in LM -->
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<p>When music is printed, a lot of notational elements must be added to the
output. For example, compare the input and output of the following example:
<blockquote>
<pre class="verbatim">
cis4 cis2. g4
</pre>
<p>
<a href="../b7/lily-2876d60a.ly">
<img align="middle"
border="0" src="../b7/lily-2876d60a.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>The input is rather sparse, but in the output, bar lines, accidentals,
clef, and time signature are added. LilyPond <em>interprets</em> the
input. During this step, the musical information is inspected in time
order, similar to reading a score from left to right. While reading
the input, the program remembers where measure boundaries are, and which
pitches require explicit accidentals. This information can be presented on
several levels. For example, the effect of an accidental is limited
to a single staff, while a bar line must be synchronized across the
entire score.
<p>Within LilyPond, these rules and bits of information are grouped in
<em>Contexts</em>. Some examples of contexts are <code>Voice</code>,
<code>Staff</code>, and <code>Score</code>. They are hierarchical, for
example: a <code>Staff</code> can contain many <code>Voice</code>s, and a
<code>Score</code> can contain many <code>Staff</code> contexts.
<blockquote>
<img src="../context-example.png" alt="context-example.png">
</blockquote>
<p>Each context has the responsibility for enforcing some notation rules,
creating some notation objects and maintaining the associated
properties. For example, the <code>Voice</code> context may introduce an
accidental and then the <code>Staff</code> context maintains the rule to
show or suppress the accidental for the remainder of the measure. The
synchronization of bar lines is handled at <code>Score</code> context.
<p>However, in some music we may not want the bar lines to be
synchronized – consider a polymetric score in 4/4 and 3/4 time. In
such cases, we must modify the default settings of the <code>Score</code>
and <code>Staff</code> contexts.
<p>For very simple scores, contexts are created implicitly, and you need
not be aware of them. For larger pieces, such as anything with more
than one staff, they must be
created explicitly to make sure that you get as many staves as you
need, and that they are in the correct order. For typesetting pieces
with specialized notation, it can be useful to modify existing or
to define new contexts.
<p>A complete description of all available contexts is in the program
reference, see
<a name="index-Contexts-2744"></a><a href="../lilypond-internals/Contexts.html#Contexts">Contexts</a>.
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Up: <a rel="up" accesskey="u" href="Discussion-of-specific-tweaks.html#Discussion-of-specific-tweaks">Discussion of specific tweaks</a>
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