What's a well-formatted date? ``` <datetime literal> ::= <date literal> | <time literal> | <timestamp literal> <date literal> ::= DATE <date string> <time literal> ::= TIME <time string> <timestamp literal> ::= TIMESTAMP <timestamp string> <date string> ::= <quote> <date value> <quote> <time string> ::= <quote> <time value> [ <time zone interval> ] <quote> <timestamp string> ::= <quote> <date value> <space> <time value> [ <time zone interval> ] <quote> <time zone interval> ::= 90 Database Language SQL X3H2-92-154/DBL CBR-002 5.3 <literal> <sign> <hours value> <colon> <minutes value> <date value> ::= <years value> <minus sign> <months value> <minus sign> <days value> <time value> ::= <hours value> <colon> <minutes value> <colon> <seconds value> <interval literal> ::= INTERVAL [ <sign> ] <interval string> <interval qualifier> <interval string> ::= <quote> { <year-month literal> | <day-time literal> } <quote> <year-month literal> ::= <years value> | [ <years value> <minus sign> ] <months value> <day-time literal> ::= <day-time interval> | <time interval> <day-time interval> ::= <days value> [ <space> <hours value> [ <colon> <minutes value> [ <colon> <seconds value> ] ] ] <time interval> ::= <hours value> [ <colon> <minutes value> [ <colon> <seconds value> ] ] | <minutes value> [ <colon> <seconds value> ] | <seconds value> <years value> ::= <datetime value> <months value> ::= <datetime value> <days value> ::= <datetime value> <hours value> ::= <datetime value> <minutes value> ::= <datetime value> <seconds value> ::= <seconds integer value> [ <period> [ <seconds fraction> ] ] <seconds integer value> ::= <unsigned integer> <seconds fraction> ::= <unsigned integer> Lexical elements 91 X3H2-92-154/DBL CBR-002 5.3 <literal> <datetime value> ::= <unsigned integer> ```