Read the item, not a generic symbol chart
Look for a written care statement on the packaging, product page or manual. Symbols can be accompanied by conditions such as top-rack only, and an unmarked item should not be treated as safe merely because it resembles another product.
Separate multi-part items before assessing them. A container base and lid, bottle and cap, or utensil and removable handle can have different instructions. Pyrex, for example, distinguishes plastic-cover placement from glass care.
Items that deserve an extra check
Sharp kitchen knives, decorated glassware, cookware with specialized coatings, wooden pieces and insulated drinkware should be checked individually. WÜSTHOF recommends handwashing its knives; YETI publishes dishwasher directions for Rambler drinkware. Those different examples show why a blanket rule based on category alone is unreliable.
Electrical or battery-powered parts do not belong in the machine unless their maker explicitly identifies a detachable dishwasher-safe component. Keep irreplaceable, antique or unknown pieces out until their care can be established.
Load compatible items properly
Permission to machine wash does not remove the need for spacing. Secure light parts, prevent glass pieces from touching and keep all items clear of the spray arms and dispenser. Use the cycle and rack specified for the item.
When the item’s care conflicts with the appliance’s available settings, use the item’s permitted alternative cleaning method. Do not choose a hotter cycle simply to compensate for a tightly packed load.