1 files changed, 96 insertions, 0 deletions
diff --git a/layout/style/nsIStyleRule.h b/layout/style/nsIStyleRule.h
new file mode 100644
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+++ b/layout/style/nsIStyleRule.h
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * internal abstract interface for objects providing immutable style
+ * information
+ */
+
+#ifndef nsIStyleRule_h___
+#define nsIStyleRule_h___
+
+#include <stdio.h>
+
+#include "nsCSSPropertyID.h"
+#include "nsISupports.h"
+
+class nsCSSValue;
+struct nsRuleData;
+
+// IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}
+#define NS_ISTYLE_RULE_IID     \
+{ 0xf75f3f70, 0x435d, 0x43a6, \
+ { 0xa0, 0x1b, 0x65, 0x97, 0x04, 0x89, 0xca, 0x26 } }
+
+/**
+ * An object implementing |nsIStyleRule| (henceforth, a rule) represents
+ * immutable stylistic information that either applies or does not apply
+ * to a given element.  It belongs to an object or group of objects that
+ * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
+ * sheet).
+ *
+ * A rule becomes relevant to the computation of style data when
+ * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
+ * points to the rule.  (A rule node, |nsRuleNode|, is a node in the
+ * rule tree, which is a lexicographic tree indexed by rules.  The path
+ * from the root of the rule tree to the |nsRuleNode| for a given
+ * |nsStyleContext| contains exactly the rules that match the element
+ * that the style context is for, in priority (weight, origin,
+ * specificity) order.)
+ *
+ * The computation of style data uses the rule tree, which calls
+ * |nsIStyleRule::MapRuleInfoInto| below.
+ *
+ * It is worth emphasizing that the data represented by a rule
+ * implementation are immutable.  When the data need to be changed, a
+ * new rule object must be created.  Failing to do this will lead to
+ * bugs in the handling of dynamic style changes, since the rule tree
+ * caches the results of |MapRuleInfoInto|.
+ *
+ * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
+ * to typically being owned by their sheet), which are in turn garbage
+ * collected (with the garbage collection roots being style contexts).
+ */
+
+
+class nsIStyleRule : public nsISupports {
+public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
+
+  /**
+   * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
+   * data represented by the rule that:
+   *   + are relevant for any structs in |aRuleData->mSIDs| (style
+   *     struct ID bits)
+   *   + are not already filled into the data struct
+   * into the appropriate data struct in |aRuleData|.  It is important
+   * that only empty data are filled in, since the rule tree is walked
+   * from highest priority rule to least, so that the walk can stop if
+   * all needed data are found.  Thus overwriting non-empty data will
+   * break CSS cascading rules.
+   */
+  virtual void MapRuleInfoInto(nsRuleData* aRuleData)=0;
+
+  /**
+   * Returns whether this style rule has any style data for inherited
+   * properties.
+   */
+  virtual bool MightMapInheritedStyleData() = 0;
+
+  /**
+   * Gets and sets given aProperty's value to aValue.
+   * Returns true, if aValue is filled in this rule.
+   */
+  virtual bool GetDiscretelyAnimatedCSSValue(nsCSSPropertyID aProperty,
+                                             nsCSSValue* aValue) = 0;
+
+#ifdef DEBUG
+  virtual void List(FILE* out = stdout, int32_t aIndent = 0) const = 0;
+#endif
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)
+
+#endif /* nsIStyleRule_h___ */