| Index: sky/sdk/lib/framework/node.dart
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| diff --git a/sky/sdk/lib/framework/node.dart b/sky/sdk/lib/framework/node.dart
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| index 44c14fe5edfde4cd3f5c68e89b4a3382dedfd1f6..8e772a9d3be4b79a5da20c790d06046a567d92be 100644
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| --- a/sky/sdk/lib/framework/node.dart
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| +++ b/sky/sdk/lib/framework/node.dart
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| @@ -1,15 +1,33 @@
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| class AbstractNode {
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| - // Nodes always have a 'depth' greater than their ancestors'.
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| - // There's no guarantee regarding depth between siblings. The depth
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| - // of a node is used to ensure that nodes are processed in depth
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| - // order. The 'depth' of a child can be more than one greater than
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| - // the 'depth' of the parent, because the 'depth' values are never
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| - // decreased: all that matters is that it's greater than the parent.
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| - // Consider a tree with a root node A, a child B, and a grandchild
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| - // C. Initially, A will have 'depth' 0, B 'depth' 1, and C 'depth'
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| - // 2. If C is moved to be a child of A, sibling of B, then the
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| - // numbers won't change. C's 'depth' will still be 2.
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| + // AbstractNode represents a node in a tree.
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| + // The AbstractNode protocol is as follows:
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| + // - When a subclass is changing the parent of a child, it should
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| + // call either parent.adoptChild(child) or parent.dropChild(child)
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| + // as appropriate. Subclasses should expose an API for
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| + // manipulating the tree if you want to (e.g. a setter for a
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| + // 'child' property, or an 'add()' method to manipulate a list).
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| + // - You can see the current parent by querying 'parent'.
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| + // - You can see the current attachment state by querying
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| + // 'attached'. The root of any tree that is to be considered
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| + // attached should be manually attached by calling 'attach()'.
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| + // Other than that, don't call 'attach()' or 'detach()'. This is
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| + // all managed automatically assuming you call the 'adoptChild()'
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| + // and 'dropChild()' methods appropriately.
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| + // - Subclasses that have children must override 'attach()' and
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| + // 'detach()' as described below.
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| + // - Nodes always have a 'depth' greater than their ancestors'.
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| + // There's no guarantee regarding depth between siblings. The
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| + // depth of a node is used to ensure that nodes are processed in
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| + // depth order. The 'depth' of a child can be more than one
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| + // greater than the 'depth' of the parent, because the 'depth'
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| + // values are never decreased: all that matters is that it's
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| + // greater than the parent. Consider a tree with a root node A, a
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| + // child B, and a grandchild C. Initially, A will have 'depth' 0,
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| + // B 'depth' 1, and C 'depth' 2. If C is moved to be a child of A,
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| + // sibling of B, then the numbers won't change. C's 'depth' will
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| + // still be 2. This is all managed automatically assuming you call
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| + // 'adoptChild()' and 'dropChild()' appropriately.
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| int _depth = 0;
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| int get depth => _depth;
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