in regex how to specify number of occurrence code example

Example 1: numbered occurences in regex

/^[a-z]{0,10}$/

{3} exactly 3
{6,} at least 6
{2,5} 2 to 5

Example 2: javascript regex Zero or one occurrence

// javascript regex Zero or one occurrence
let neighbor = /neighbou?r/;
console.log(neighbor.test("neighbour")); // true
console.log(neighbor.test("neighbor")); // true