def content(tokens, base_url):
    """``content`` property validation."""
    # See https://www.w3.org/TR/css-content-3/#content-property
    tokens = list(tokens)
    parsed_tokens = []
    while tokens:
        if len(tokens) >= 2 and (
                tokens[1].type == 'literal' and tokens[1].value == ','):
            token, tokens = tokens[0], tokens[2:]
            parsed_token = (
                get_image(token, base_url) or get_url(token, base_url))
            if parsed_token:
                parsed_tokens.append(parsed_token)
            else:
                return
        else:
            break
    if len(tokens) == 0:
        return
    if len(tokens) >= 3 and tokens[-1].type == 'string' and (
            tokens[-2].type == 'literal' and tokens[-2].value == '/'):
        # Ignore text for speech
        tokens = tokens[:-2]
    keyword = get_single_keyword(tokens)
    if keyword in ('normal', 'none'):
        return (keyword,)
    return get_content_list(tokens, base_url)
``content`` property validation.
weasyprint/css/validation/properties.py