Active Block Modifiers: Improve grammar, and clarify some points

en/chapters/abms.md

@@ -6,20 +6,19 @@ root: ../../
 
 ## Introduction
 
-In this chapter we will learn how to create an **A**ctive **B**lock **M**odifier (**ABM**).
-An active block modifier allows you to run code on certain nodes at certain
-intervals.
-Please be warned, ABMs which are too frequent or act on too many nodes cause
-massive amounts of lag. Use them lightly.
+An active *A**ctive **B**lock **M**odifier (**ABM**) allows you to run code on
+certain nodes at specific intervals.
+Please be warned, ABMs which are too frequent or act on a large number of nodes
+cause massive amounts of lag. Use them sparingly.
 
 * Special Growing Grass
 * Your Turn
 
 ## Special Growing Grass
 
-We are now going to make a mod (yay!).
-It will add a type of grass called alien grass - it grows near water on grassy
-blocks.
+If you want to make a mod that adds a type of grass called alien grass
+- it grows near water on grassy blocks - you first register the grass, then
+write an ABM.
 
 {% highlight lua %}
 minetest.register_node("aliens:grass", {
@@ -41,12 +40,17 @@ minetest.register_abm({
 })
 {% endhighlight %}
 
-Every ten seconds the ABM is run. Each node which has the correct nodename and
-the correct neighbors then has a 1 in 5 chance of being run. If  a node is run on,
-an alien grass block is placed above it. Please be warned, that will delete any
-blocks above grass blocks - you should check there is space by doing minetest.get_node.
+This ABM runs every ten seconds. There is a 1 in 5 chance of the ABM running on each
+node that has the correct name and the correct neighbors. If the ABM runs on a
+node, an alien grass node is placed above it. Please be warned, this will delete any
+node previously located in that position. To prevent this you should include a check
+using minetest.get_node to make sure there is space for the grass.
 
-That's really all there is to ABMs. Specifying a neighbor is optional, so is chance.
+Specifying a neighbor is optional. If you specify multiple neighbors, only one of them
+needs to be present to meet the requirements.
+
+Specifying chance is also optional. If you don't specify the chance, the ABM will
+always run when the other conditions are met. 
 
 ## Your Turn