Comment 1 for bug 41290

Suggested Fix:

Fix duplicated lines.

Append a comment block to the top of the file, describing what the file is and where to find more information. This could include a pointer to the man page so that newbies know where to start looking. Append another block to the bottom of the file with a brief overview of the file's syntax. In this second block, disect the two standard lines that are nearly always in the file (dapper main restricted)

Suggestion:
## Package Resource List for APT
# The package resource list is used to locate archives of the package
# distribution system in use on the system.
#
# The source list is designed to support any number of active sources and
# a variety of source media. The file lists one source per line, with the
# most preferred source listed first. Lines or parts of lines may be
# marked as comments with the # (hash) character.
#
# More detailed information about the syntax of this file may be found at
# the end of this file or in sources.list(5)
#
# After editing this file, you should do "apt-get update" to resynchronize
# your package indexes.
#
# /etc/apt/sources.list
###

...
file content
...

## Source Line Syntax
#
# [type] [URI] [distribution] [component1 [component2 component3..]]
#
# type - Either "deb" or "deb-src", indicating whether the source
# provides packages or sources.
# URI - A Universal Resource Identifier (URI), which is a superset of the
# more specific and well-known Universal Resource Locator, or URL.
# See sources.list(5) for a detailed specification of this URI.
# distribution - The name of the distribution folder in the repository
# that the components are located in.
# components - One or more components that packages/sources should be
# downloaded from.
#
# Examples:
# This file ships with two lines similar to the following:
#
# deb http://archive.ubuntu.com/ubuntu/ dapper main restricted
# deb-src http://archive.ubuntu.com/ubuntu/ dapper main restricted
#
# These two lines tell APT to download packages and sources from the
# 'main' and 'restricted' components found in the 'dapper' distribution
# at 'http://archive.ubuntu.com/ubuntu/', a Internet URL.
###