Dryml rexml CONST NAME_STR not loading

[iox]

Not sure why, but a legacy project suddenly failed to restart with the following error:

/var/lib/gems/2.3.0/gems/bundler-1.16.0/lib/bundler/runtime.rb:84:in rescue in block (2 levels) in require': There was an error while trying to load the gem 'hobo'. (Bundler::GemRequireError)
Gem Load Error is: uninitialized constant Dryml::Parser::BaseParser::NAME_STR
Backtrace for gem load error is:
/home/donations/app/vendor/bundle/ruby/2.3.0/gems/dryml-2.1.1/lib/dryml/parser/base_parser.rb:9:in <class:BaseParser>'
/home/donations/app/vendor/bundle/ruby/2.3.0/gems/dryml-2.1.1/lib/dryml/parser/base_parser.rb:3:in <module:Parser>'
/home/donations/app/vendor/bundle/ruby/2.3.0/gems/dryml-2.1.1/lib/dryml/parser/base_parser.rb:1:in <top (required)>'

It seems like the REXML base parser does not have some of these constants anymore?

As a quick workaround, I opened ./vendor/bundle/ruby/2.3.0/gems/dryml-2.1.1/lib/dryml/parser/base_parser.rb and I added some constants from the REXML base parser at the top of the file:

module Dryml::Parser

  class BaseParser < REXML::Parsers::BaseParser
      LETTER = '[:alpha:]'
      DIGIT = '[:digit:]'

      COMBININGCHAR = '' # TODO
      EXTENDER = ''      # TODO

      NCNAME_STR= "[#{LETTER}_:][-[:alnum:]._:#{COMBININGCHAR}#{EXTENDER}]*"
      NAME_STR= "(?:(#{NCNAME_STR}):)?(#{NCNAME_STR})"
      UNAME_STR= "(?:#{NCNAME_STR}:)?#{NCNAME_STR}"