Looking for missing or superfluous images

# Pattern to match lines ending with whitespace.

P_TRAILING_WHITESPACE = re.compile(r'\s+$')

# Pattern to match figure references in HTML.

P_FIGURE_REFS = re.compile(r'<img[^>]+src="([^"]+)"[^>]*>')

# What kinds of blockquotes are allowed?

KNOWN_BLOCKQUOTES = {

    'callout',

    for filename in docs.keys():

        checker = create_checker(args, filename, docs[filename])

        checker.check()

    check_figures(args.source_dir, args.reporter)

    args.reporter.report()

                   seen)

def check_figures(source_dir, reporter):

    """Check that all figures are present and referenced."""

    # Get references.

    try:

        all_figures_html = os.path.join(source_dir, '_includes', 'all_figures.html')

        with open(all_figures_html, 'r') as reader:

            text = reader.read()

        figures = P_FIGURE_REFS.findall(text)

        referenced = [os.path.split(f)[1] for f in figures if '/fig/' in f]

    except FileNotFoundError as e:

        reporter.add(all_figures_html,

                     'File not found')

        return

    # Get actual files.

    fig_dir_path = os.path.join(source_dir, 'fig')

    actual = [f for f in os.listdir(fig_dir_path) if not f.startswith('.')]

    # Report differences.

    unexpected = set(actual) - set(referenced)

    reporter.check(not unexpected,

                   None,

                   'Unexpected image files: {0}',

                   ', '.join(sorted(unexpected)))

    missing = set(referenced) - set(actual)

    reporter.check(not missing,

                   None,

                   'Missing image files: {0}',

                   ', '.join(sorted(missing)))

def create_checker(args, filename, info):

    """Create appropriate checker for file."""