* HEADER-NAME name a header, where all blanks character sequence are
considered as just one space character.
+ HEADER-NAME can optionnaly be followed by one of the following
+ extension to match a subset of the text in the header:
+
+ - '.raw' do nothing.
+ - '.name' extract the name part.
+ - '.address' extract the email address part.
+ - '.user' extract the username before the @ in email address.
+ - '.domain' extract the domain name of the email address.
+
+ Example with header 'From: Frederic Jolliton <frederic@jolliton.com>, a@b.c (Foo)':
+
+ 'From.name' -> [ 'Frederic Jolliton' , 'Foo' ]
+ 'From.address' -> [ 'frederic@jolliton.com' , 'a@b.c' ]
+ 'From.user' -> [ 'frederic' , 'a' ]
+ 'From.domain' -> [ 'jolliton.com' , 'b.c' ]
+
* MATCH-TYPE give the type of match to perform against the header.
Each match type take an argument.