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Björn Höhrmann > CSS-SAC > CSS::SAC::Condition



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Module Version: 0.03   Source  


CSS::SAC::Condition - base class for SAC conditions


  use CSS::SAC::Condition qw(:constants);
  foo if $cond->is_type(CONDITION_TYPE_CONSTANT);


SAC Conditions describe conditions that can be expressed in CSS such as AttributeConditions or PositionalConditions. This class provides everything that is needed to implement simple conditions (methods, constants) as well as what is needed by subclasses defining more complex conditions.

The constants are those defined in the SAC spec, with the leading SAC_ removed. What the constants map to is to be considered an opaque token that can be tested for equality. If there is demand for it, I will add a way to add new constants (for people wishing to define new condition types).

I have also added the UNKNOWN_CONDITION constant. It shouldn't occur in normal processing but it's always useful to have such fallback values.

The Condition interface adds $cond->is_type($condition_type) to the interface defined in the SAC spec. This allows for more flexible type checking. For instance, if you create a subclass of ContentCondition that extends it with the ContentRegexCondition interface you will probably want software ignorant of your subclass's existence to still be able to do something useful with it. That software should also be able to treat ContentRegexConditions as if they were ContentConditions.

If that software tests condition types the following way:

  $rcond->ConditionType == CONTENT_CONDITION

then you've lost because the condition type of ContentRegexCondition is REGEX_CONTENT_CONDITION. If, however, it tests it that way:


then you can simply implement is_type() so that it returns true for it's own type and the type of it's superclass. I strongly recommend using the latter scheme except in cases when you want to know the exact type.




Robin Berjon <>

This module is licensed under the same terms as Perl itself.

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