class SyntaxTree::Parser::MultiByteString

the index of the character within the string.
build up an array of indices, such that array will be equal to
that there are characters in the string that are multi-byte, so we will
Represents a line in the source. If this class is being used, it means

def [](byteindex)

to compare it to 0 here.
there's a BOM at the beginning of the file, which is the reason we need
Technically it's possible for the column index to be a negative value if 
def [](byteindex)
  indices[[byteindex, 0].max]
end

def initialize(start, line) 

def initialize(start, line)
  @start = start
  @indices = []
  line
    .each_char
    .with_index(start) do |char, index|
      char.bytesize.times { @indices << index }
    end
end