String CRAWLER_DOCUMENT_SPACE_CHARS = "crawler.document.space.chars";

    /** The key of the configuration. e.g. u002eu06d4u2e3cu3002 */
    String CRAWLER_DOCUMENT_FULLSTOP_CHARS = "crawler.document.fullstop.chars";

    /** The key of the configuration. e.g. UTF-8 */
    String CRAWLER_CRAWLING_DATA_ENCODING = "crawler.crawling.data.encoding";

<p>
An unrecognized character following a backslash in a rune literal is illegal.
</p>

<pre class="ebnf">
rune_lit         = "'" ( unicode_value | byte_value ) "'" .
unicode_value    = unicode_char | little_u_value | big_u_value | escaped_char .
byte_value       = octal_byte_value | hex_byte_value .
octal_byte_value = `\` octal_digit octal_digit octal_digit .
hex_byte_value   = `\` "x" hex_digit hex_digit .