achievementID - The numeric ID of an achievement (number)
index - Index of one of the achievement's criteria (between 1 and GetAchievementNumCriteria()) (number)
statisticID - The numeric ID of a statistic (number)
Returns:
description - Description of the criterion (as displayed in the UI for achievements with multiple criteria) or statistic (string)
type - Type of criterion: a value of 8 indicates the criterion is another achievement; other values are not used in the default UI (number)
completed - True if the player has completed the criterion; otherwise false (boolean)
quantity - If applicable, number of steps taken towards completing the criterion (e.g. for the only criterion of "Did Somebody Order a Knuckle Sandwich?", the player's current Unarmed skill; for the first criterion of "Pest Control", 1 if the player has killed an Adder, 0 otherwise (number)
requiredQuantity - If applicable, number of steps required to complete the criterion (e.g. 400 for the only criterion of "Did Somebody Order a Knuckle Sandwich?"; 1 for any criterion of "Pest Control" (number)
characterName - Character name with which the criterion was completed. Currently always the player character's name for completed criteria (string)
flags - Test against the following masks with bit.band() to reveal additional information: (bitfield)
0x00000001 - Criterion should be displayed as a progress bar
0x00000002 - Criterion should be hidden in normal achievement displays
assetID - Internal ID number of the quest to complete, NPC to kill, item to acquire, world object to interact with, achievement to earn, or other game entity related to completing the criterion. (Note: some but not all of these ID types are usable elsewhere in the WoW API) (number)
quantityString - Text to be shown when displaying quantity and requiredQuantity in a UI element. (Not always the same as format("%d / %d", quantity, requiredQuantity); e.g. "Got My Mind On My Money" shows monetary amounts with embedded textures for gold, silver, and copper) (string)
criteriaID - Unique ID number identifying the criterion; usable with GetAchievementInfoFromCriteria() (number)
