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Extended Regular Expressions (EREs) will support Basic Regular Expressions (BREs are essentially a subset of EREs).
It is therefore important to recognise how often everyday life is disrupted by migraine and keep a record of how many days per month you have a headache.
If this is more than half the month, you may well have chronic migraine and should see a neurologist, as he or she may be able to offer you a wider range of treatments to help reduce your symptoms.
However for some people there is a steady progression in headache frequency, especially in long term sufferers.
Most applications, utilities and laguages that implement RE's, especially PERL, extend the ERE capabilities and what are typically called PERL Compatible Regular Expressions (PCREs) have, largely, become a de facto standard.
Implementation documentation should always be consulted in case some wierd Regular Expression variant is involved.
People with chronic migraine are three times more likely to consult their GPs compared to episodic migraine.
In the UK 43% of people with chronic migraine visit a neurologist or headache specialist compared to only 18% of people with episodic migraine.