Example
let string1 = "Hello" //simple string
let string2 = "Line\nNewLine" //string with newline escape sequence
let string3 = @"Line\nSameLine" //use @ to create a verbatim string literal
let string4 = @"Line""with""quoutes inside" //double quoute to indicate a single quoute inside @ string
let string5 = """single "quote" is ok""" //triple-quote string literal, all symbol including quote are verbatim
let string6 = "ab
cd"// same as "ab\ncd"
let string7 = "xx\
yy" //same as "xxyy", backslash at the end contunies the string without new line, leading whitespace on the next line is ignored
