Explanation of trim level differences between Erubis and the ERB when Rails used both.

console.rb

irb(main):045:0> ERB.new("<% if true -%>\nhi\n<% else %>\nbye\n<% end %>", nil, "-").result # old rails with '-'
=> "hi\n"
irb(main):047:0> ERB.new("<% if true %>\nhi\n<% else %>\nbye\n<% end %>", nil, "-").result # old rails without '-'
=> "\nhi\n"
irb(main):048:0> Erubis::Eruby.new("<% if true %>\nhi\n<% else %>\nbye\n<% end %>").result # new rails with Erubis default trim
=> "hi\n"
irb(main):049:0> Erubis::Eruby.new("<% if true %>\nhi\n<% else %>\nbye\n<% end %>", trim: false).result # Erubis with trimming turned off
=> "\nhi\n"