The notes here are for JavaScript but there will be equivalents in other languages.

Multiline

m modifier for multiline searches.

Do a multiline search for “is” at the beginning of each line in a string:

const str = "\nIs th\nis it?";
const patt1 = /^is/m;

The m modifier treat beginning (^) and end ($) characters to match the beginning or end of each line of a string (delimited by \n or \r), rather than just the beginning or end of the string.

Global

g modified

const str = "Is this all there is?";
const patt1 = /is/g;

The g modifier is used to perform a global match (find all matches rather than stopping after the first match).

Insensitive

i modifier

Do a case-insensitive search for “w3schools” in a string:

var str = "Visit W3Schools";
var patt1 = /w3schools/i;