2. Selectors and filtering

$("#orderForm")                 // id
$(".order-row")                 // class
$("table tr:even")              // jQuery extension pseudo-selector (avoid for performance; use CSS where possible)
$("input[type='email']")        // attribute
$("ul > li:first-child")        // CSS
$("#orders").find(".paid")      // descendant search — faster than one complex selector
$(".item").filter(".active")    // narrow a set
$(".item").not(".disabled")
$(".item").eq(2)                // third element
$(".item").first() / .last()
$("li").has("ul")               // contains matching descendants
$("#el").is(":visible")         // test → boolean

const $rows = $(".order-row");   // cache selections (prefix $ by convention)
const raw = $rows[0];            // or $rows.get(0) → plain DOM element
$(raw)                           // wrap a DOM element