restructuring to separate language from API

docs/blocks/variables/var.md

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+# Local Variables
+
+How to define and use local variables.
+
+### @parent language
+
+A variable is a place where you can store and retrieve data. Variables have a name, a [type](/reference/types), and value:
+
+* *name* is how you'll refer to the variable
+* *type* refers to the kind of data a variable can store
+* *value* refers to what's stored in the variable
+
+### Var statement
+
+Use the Block Editor variable statement to create a variable 
+and the [assignment operator](/blocks/variables/assign) 
+to store something in the variable.
+
+For example, this code stores the number `2` in the `x` variable:
+
+```blocks
+let x = 2;
+```
+Here's how to define a variable in the Block Editor:
+
+1. Click `variables`.
+
+2. Change the default variable name if you like.
+
+3. Drag a block type on the right-side of the [assignment operator](/blocks/variables/assign) and click the down arrow to change the variable name.
+
+A variable is created for the number returned by the [brightness](/reference/led/brightness) function.
+
+```blocks
+let b = led.brightness();
+```
+
+### Using variables
+
+Once you've defined a variable, just use the variable's name whenever you need what's stored in the variable. For example, the following code shows the value stored in `counter` on the LED screen:
+
+```blocks
+let counter = 1;
+basic.showNumber(counter);
+```
+
+To change the contents of a variable use the assignment operator. The following code sets `counter` to 1 and then increments `counter` by 10:
+
+```blocks 
+let counter = 1;
+counter = counter + 10;
+basic.showNumber(counter);
+```
+
+### Why use variables?
+
+If you want to remember and modify data, you'll need a variable. 
+A counter is a great example:
+
+```blocks
+let counter = 0;
+input.onButtonPressed(Button.A, () => { 
+  counter = counter + 1;
+  basic.showNumber(counter);
+});
+```
+
+### Local variables
+
+Local variables exist only within the function or block of code where they're defined. For example:
+
+```blocks
+// x does NOT exist here.
+if (led.brightness() > 128) {
+  // x exists here
+  let x = 0;
+}
+```
+
+#### Notes
+
+* You can use the default variable names if you'd like, however, it's best to use descriptive variable names. To change a variable name in the editor, select the down arrow next to the variable and then click "new variable".
+
+### See also
+
+[types](/reference/types), [assignment operator](/blocks/variables/assign)
+