class Asciidoctor::PreprocessorReader

def resolve_include_path target, attrlist, attributes

relative to the outermost document. May also return a boolean to halt processing of the include.
Returns An Array containing the resolved (absolute) include path, the target type, and the path

attributes - A Hash of attributes parsed from attrlist.
attrlist - An attribute list String (i.e., the text between the square brackets).
(Attribute references in target value have already been resolved).
target - A String containing the unresolved include target.

environment.
This method is overridden in Asciidoctor.js to resolve the target of an include in the browser

cursor should be advanced beyond this line (true) or the line should be reprocessed (false).
return a boolean to halt processing of the include directive line and to indicate whether the
and the path of the target relative to the outermost document. Alternately, the method may
Array containing the resolved (absolute) path of the target, the target type (:file or :uri),
An internal method to resolve the target of an include directive. This method must return an

Internal: Resolve the target of an include directive. 
def resolve_include_path target, attrlist, attributes
  doc = @document
  if (Helpers.uriish? target) || (::String === @dir ? nil : (target = %(#{@dir}/#{target})))
    return replace_next_line %(link:#{target}[#{attrlist}]) unless doc.attr? 'allow-uri-read'
    if doc.attr? 'cache-uri'
      # caching requires the open-uri-cached gem to be installed
      # processing will be automatically aborted if these libraries can't be opened
      Helpers.require_library 'open-uri/cached', 'open-uri-cached' unless defined? ::OpenURI::Cache
    elsif !RUBY_ENGINE_OPAL
      # autoload open-uri
      ::OpenURI
    end
    [(::URI.parse target), :uri, target]
  else
    # include file is resolved relative to dir of current include, or base_dir if within original docfile
    inc_path = doc.normalize_system_path target, @dir, nil, target_name: 'include file'
    unless ::File.file? inc_path
      if attributes['optional-option']
        logger.info { message_with_context %(optional include dropped because include file not found: #{inc_path}), source_location: cursor }
        shift
        return true
      else
        logger.error message_with_context %(include file not found: #{inc_path}), source_location: cursor
        return replace_next_line %(Unresolved directive in #{@path} - include::#{target}[#{attrlist}])
      end
    end
    # NOTE relpath is the path relative to the root document (or base_dir, if set)
    # QUESTION should we move relative_path method to Document
    relpath = doc.path_resolver.relative_path inc_path, doc.base_dir
    [inc_path, :file, relpath]
  end
end