在RDoC(https://github.com/ruby/rdoc)的自述文件中，提供的示例在各自的行上使用两个散列/磅符号来开始注释块.这是一种要求，还是仅仅是惯例？例如(引用自述文件):
##
# This class represents an arbitrary shape by a series of points.
class Shape
##
# Creates a new shape described by a +polyline+.
#
# If the +polyline+ does not end at the same point it started at the
# first pointed is copied and placed at the end of the line.
#
# An ArgumentError is raised if the line crosses itself, but shapes may
# be concave.
def initialize polyline
# ...
end
end