Given the following test case and regular expressions, there will be an error message unmatched input. Explain what caused this error. How to correct the lexer so that it can still count the identifiers etc., even though the input contains illegal characters? %% BEGIN x1 & @ END \"[^\"]*\" {quoted string ++; } {KEYWORD} {keyword++;} [a-zA-Z][a-zA-Z0-9]* {id++;} [0-9]+ {num++;} "/**" {yybegin (comment); } "/" {yybegin (YYINITIAL);} \ {} Whether the unmatched input will occur for the following input? Explain your answer. BEGIN x1 "&" "@" END