module Asciidoctor::Substitutors

def resolve_lines_to_highlight source, spec, start = nil

Returns an [Array] of unique, sorted line numbers.

start - The line number of the first line (optional, default: false)
spec - The lines specifier (e.g., "1-5, !2, 10" or "1..5;!2;10")
source - The String source.

e.g., highlight="1-5, !2, 10" or highlight=1-5;!2,10

Public: Resolve the line numbers in the specified source to highlight from the provided spec. 
def resolve_lines_to_highlight source, spec, start = nil
  lines = []
  spec = spec.delete ' ' if spec.include? ' '
  ((spec.include? ',') ? (spec.split ',') : (spec.split ';')).map do |entry|
    if entry.start_with? '!'
      entry = entry.slice 1, entry.length
      negate = true
    end
    if (delim = (entry.include? '..') ? '..' : ((entry.include? '-') ? '-' : nil))
      from, _, to = entry.partition delim
      to = (source.count LF) + 1 if to.empty? || (to = to.to_i) < 0
      if negate
        lines -= (from.to_i..to).to_a
      else
        lines |= (from.to_i..to).to_a
      end
    elsif negate
      lines.delete entry.to_i
    elsif !lines.include?(line = entry.to_i)
      lines << line
    end
  end
  # If the start attribute is defined, then the lines to highlight specified by the provided spec should be relative to the start value.
  unless (shift = start ? start - 1 : 0) == 0
    lines = lines.map {|it| it - shift }
  end
  lines.sort
end