What is the syntax for a multiline string literal?

All string literals can be broken across several lines; for example:

let string = "line one
line two";

is a two line string, the same as "line one\nline two" (of course one can use the \n newline escape directly too). If you wish to just break a string across multiple lines for formatting reasons you can escape the newline and leading whitespace with a \; for example:

let string = "one line \
    written over \
    several";

is the same as "one line written over several".

If you want linebreaks in the string you can add them before the \:

let string = "multiple\n\
              lines\n\
              with\n\
              indentation";

It’s the same as "multiple\nlines\nwith\nindentation";