begin
alpha = "a-zA-Z"
digit = "0-9"
atext = "[#{alpha}#{digit}\!\#\$\%\&\'\*+\/\=\?\^\_\`\{\|\}\~\-]"
dot_atom_text = "#{atext}+([.]#{atext}*)*"
dot_atom = "#{dot_atom_text}"
qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]'
text = "[\\x01-\\x09\\x11\\x12\\x14-\\x7f]"
quoted_pair = "(\\x5c#{text})"
qcontent = "(?:#{qtext}|#{quoted_pair})"
quoted_string = "[\"]#{qcontent}+[\"]"
atom = "#{atext}+"
word = "(?:#{atom}|#{quoted_string})"
obs_local_part = "#{word}([.]#{word})*"
local_part = "(?:#{dot_atom}|#{quoted_string}|#{obs_local_part})"
no_ws_ctl = "\\x01-\\x08\\x11\\x12\\x14-\\x1f\\x7f"
dtext = "[#{no_ws_ctl}\\x21-\\x5a\\x5e-\\x7e]"
dcontent = "(?:#{dtext}|#{quoted_pair})"
domain_literal = "\\[#{dcontent}+\\]"
obs_domain = "#{atom}([.]#{atom})*"
domain = "(?:#{dot_atom}|#{domain_literal}|#{obs_domain})"
addr_spec = "#{local_part}\@#{domain}"
pattern = /^#{addr_spec}$/
end