Support for the Ruby 2.4 series has ended. See here for reference.
<!ENTITY name SYSTEM
“…”> <!ENTITY name “…”>
# File rexml/dtd/entitydecl.rb, line 14 def initialize src super() md = nil if src.match( PUBLIC ) md = src.match( PUBLIC, true ) @middle = "PUBLIC" @content = "#{md[2]} #{md[4]}" elsif src.match( SYSTEM ) md = src.match( SYSTEM, true ) @middle = "SYSTEM" @content = md[2] elsif src.match( PLAIN ) md = src.match( PLAIN, true ) @middle = "" @content = md[2] elsif src.match( PERCENT ) md = src.match( PERCENT, true ) @middle = "" @content = md[2] end raise ParseException.new("failed Entity match", src) if md.nil? @name = md[1] end