For multi select with more script options. If you want to select more options, you must hold CTRL key. (default select behaviour)

Check out Github

Example 1

Simple select, no mutiple

Example 2

Multiple select of size 7 with group counter. Second select is cleared, when first changed.

Example 3

Multiple select with group counter. You can select maximum 2 options of all categories.

Example 4

Multiple select with group counter. You can select maximum 3 options ONLY from one category.