Chance of drop is done in percentage where on the game it is done in ratios. This is simply done for the players.

Example 1:

<actorType name="Skeleton" id="3" tile="19" width="1" height="1" minItems="0" maxItems="2" exp="155" kingdom="undead" >
<statistics health="5" charge="0" level="1" attack="2" defence="2" />
<itemChance name="null" chance="6" />
<itemChance name="Apple" chance="1" />
<itemChance name="Red Potion" chance="1" />
<itemChance name="Leather Helmet" chance="1" min="1" max="1" />

This monster can hold between 0 to 2 items at any given time. Null which is a programmer way of saying nothing means that nothing will be given. If you add the chances up you will have 9. You will have 1/9 to get an item while 6/9 of getting nothing and even then the cap of two items may stop you from getting what you want. With this in mind there no possibile way to get the correct percentage when it comes to a player obtaining an item.

Example 2:

<actorType name="Ettin Guard" id="27" tile="11" width="1" height="1" minItems="0" maxItems="3" exp="478" kingdom="orc" >
<statistics health="25" charge="0" level="1" attack="8" defence="8" zen="0" rage="20" />
<item name="Sword" />
<itemChance name="Leather Armor" chance="1" />
<itemChance name="Gold" chance="1" min="10" max="20" />
<itemChance chance="30" />
<item name="Round Shield" onein="400" />

Notice there is an itemchance of 30. That is the same as null. Sword don't have a chance of being drop but will in fact always be dropped. Round Shield is the same but with it own chance which is 1/400. Anything that is automatically given to the player don't seem to follow the minitems and maxitems so in this case it is possible to get four items where the max is 3. Usually on this wiki if there a 100% chance then that means it can be disregarded from the min/max items.

Example 3:

<level id="Aria-7" key="true" legend="Golem" tileset="16" chests="8" width="50" height="50" rooms="30" minMonsters="1" maxMonsters="1" >
<monsterChance type="Kobold" chance="1" />
<monsterChance type="Skeleton" chance="1" />
<monster type="Skeleton Archer" count="1" />
<chest minItems="1" maxItems="2" >
<itemChance name="Ruby" chance="1" />
<itemChance name="Blue Potion" chance="5" />
<itemChance name="Gem" chance="1" />
<itemChance name="Green Potion" chance="1" />
<itemChance name="Longsword" chance="1" />
<itemChance name="Composite Bow" chance="1" />
<itemChance name="Frost Bolt" chance="1" />

Note there a monster min/max and a chest min/max plus a limited amount of chest per floor. Using what you know, you should be able to find out the chances of what monsters will be showing up per room and what items you will find in chests.