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37 :
38 : /*
39 : * internal abstract interface for objects providing immutable style
40 : * information
41 : */
42 :
43 : #ifndef nsIStyleRule_h___
44 : #define nsIStyleRule_h___
45 :
46 : #include <stdio.h>
47 :
48 : #include "nsISupports.h"
49 :
50 : struct nsRuleData;
51 :
52 : // IID for the nsIStyleRule interface {f75f3f70-435d-43a6-a01b-65970489ca26}
53 : #define NS_ISTYLE_RULE_IID \
54 : { 0xf75f3f70, 0x435d, 0x43a6, \
55 : { 0xa0, 0x1b, 0x65, 0x97, 0x04, 0x89, 0xca, 0x26 } }
56 :
57 : /**
58 : * An object implementing |nsIStyleRule| (henceforth, a rule) represents
59 : * immutable stylistic information that either applies or does not apply
60 : * to a given element. It belongs to an object or group of objects that
61 : * implement |nsIStyleSheet| and |nsIStyleRuleProcessor| (henceforth, a
62 : * sheet).
63 : *
64 : * A rule becomes relevant to the computation of style data when
65 : * |nsIStyleRuleProcessor::RulesMatching| creates a rule node that
66 : * points to the rule. (A rule node, |nsRuleNode|, is a node in the
67 : * rule tree, which is a lexicographic tree indexed by rules. The path
68 : * from the root of the rule tree to the |nsRuleNode| for a given
69 : * |nsStyleContext| contains exactly the rules that match the element
70 : * that the style context is for, in priority (weight, origin,
71 : * specificity) order.)
72 : *
73 : * The computation of style data uses the rule tree, which calls
74 : * |nsIStyleRule::MapRuleInfoInto| below.
75 : *
76 : * It is worth emphasizing that the data represented by a rule
77 : * implementation are immutable. When the data need to be changed, a
78 : * new rule object must be created. Failing to do this will lead to
79 : * bugs in the handling of dynamic style changes, since the rule tree
80 : * caches the results of |MapRuleInfoInto|.
81 : *
82 : * |nsIStyleRule| objects are owned by |nsRuleNode| objects (in addition
83 : * to typically being owned by their sheet), which are in turn garbage
84 : * collected (with the garbage collection roots being style contexts).
85 : */
86 :
87 :
88 0 : class nsIStyleRule : public nsISupports {
89 : public:
90 : NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISTYLE_RULE_IID)
91 :
92 : /**
93 : * |nsIStyleRule::MapRuleInfoInto| is a request to copy all stylistic
94 : * data represented by the rule that:
95 : * + are relevant for any structs in |aRuleData->mSIDs| (style
96 : * struct ID bits)
97 : * + are not already filled into the data struct
98 : * into the appropriate data struct in |aRuleData|. It is important
99 : * that only empty data are filled in, since the rule tree is walked
100 : * from highest priority rule to least, so that the walk can stop if
101 : * all needed data are found. Thus overwriting non-empty data will
102 : * break CSS cascading rules.
103 : */
104 : virtual void MapRuleInfoInto(nsRuleData* aRuleData)=0;
105 :
106 : #ifdef DEBUG
107 : virtual void List(FILE* out = stdout, PRInt32 aIndent = 0) const = 0;
108 : #endif
109 : };
110 :
111 : NS_DEFINE_STATIC_IID_ACCESSOR(nsIStyleRule, NS_ISTYLE_RULE_IID)
112 :
113 : #endif /* nsIStyleRule_h___ */
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