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This package and its subpackages contain classes and interfaces related
to <i>abstract syntax trees</i>.

<p>
An <i>abstract syntax tree</i> or AST represents almost every detail of
a source file in a hierarchical structure that reflects the logical
structure of the source language.
Each <i>node</i> in an AST is a type of <code>IASNode</code>.
</p>

<p>
The information stored in each node is minimal and unimportant, such as
the name of an identifier or keyword, or the text of a string literal.
It is the many different node types, and the many ways that the nodes
can be arranged -- in other words, the <i>tree shape</i> -- that
contain the semantics of the AST.
</p>

<p>
Each AST node stores location information about what source file it was in
and the offsets where it starts and ends, which is useful for IDEs.
For command-line error reporting, and for the code generation of debug
opcodes, nodes also store line and column information. Deriving line
and column from starting offset is too slow for code generation.
</p>

<p>
In order to allow an IDE to efficiently search an AST for the node
containing a particular offset, the nodes of an AST must obey the following
rules regarding location information:
<ul>
<li>Sibling nodes must not overlap and must be in offset order.</li>
<li>The start/end of a parent node must contain all its child nodes.</li>
</ul>
</p>

<p>
The immediate contents of this package is <code>ASTNodeID</code>,
an enum containing a <i>node ID</i> for every kind of AST node.
The node ID is used to identify nodes in the <code>.jbg</code> files
that create the code generator's BURM (Bottom-Up Rewrite Machine).
</p>

<p>
See the <code>org.apache.royale.compiler.tree.as</code>
and <code>org.apache.royale.compiler.tree.mxml</code> subpackages
for more information about AS and MXML trees.
</p>

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