18. An apparatus, comprising: a processor circuit, and a key terms identifying module operative on the processor circuit to retrieve a set of configuration parameters of which at least one configuration parameter comprises a value to constrain expansion of a feature of the regular expression, where the value indicates when the feature is not to be expanded, generate a set of one or more regular expression key terms from enabled features of a regular expression based on a set of configuration parameters, and filter one or more electronic messages using the set of regular expression key terms.
18. An apparatus, comprising: a processor circuit, and a key terms identifying module operative on the processor circuit to retrieve a set of configuration parameters of which at least one configuration parameter comprises a value to constrain expansion of a feature of the regular expression, where the value indicates when the feature is not to be expanded, generate a set of one or more regular expression key terms from enabled features of a regular expression based on a set of configuration parameters, and filter one or more electronic messages using the set of regular expression key terms. 19. The apparatus of claim 18 , the key terms identifying module operative to identify a set of one or more features within the regular expression enabled by the set of configuration parameters, the one or more features comprising a grouping feature, a class feature, or an operator feature.