<Append></Append>

Is a TAG that places stuff at the very bottom of a list of things.
Which depending on what you're trying to do the position of nodes matters.

Code Explanation

This is a comment. It will not be read by the game.
Basically used for Notes or a TODO list.
SAFE to delete.
Good practice to leave these for yourself.

<Append> TAG is a function in XML.
It basically adds to the end of list of things.

xpath="/blocks/block[@name='treeCactus01']"

xpath="" is another function
that looks for a specific thing in a specific directory.
It finds a Path in XML.

"/blocks/block[@name='treeCactus01']"

Is the Pathway we are targeting.
In the Vanilla blocks.xml the nodes are wrapped inside
top level node called <blocks>.

So with use the forward slash /
to tell the game to look into that node.

Then after the node name we do another forward slash /
tells the game to look at the next thing
which is a block with the name attribute treeCactus01.

With this line we are adding a Node called Drop
Which you can probably guess what it does.

On the block Destroy
it adds the item Yucca Juice to the loot list
and how many it can drop 1 to 2.
and the probability of it dropping which .2 is 20%.

</append>

Is the closing end tag.
Not all Element Nodes have an ending tag.
So you just add a forward slash / at the end.
As seen in the drop tag.

Append Notes

Image Examples

<insertAfter></insertAfter>

is a TAG that places the piece of code
After something you targeted.

You use this depending what you are doing.
As code placement matters,
depending what you're trying to do.

Example #1

<insertBefore></insertBefore>

is a TAG that places the piece of code
Before something you targeted.

You use this depending what you are doing.
As code placement matters,
depending what you're trying to do.