Some rephrasing of rang-based for docs

Author: mrotteveel

doc/sql.extensions/README.range_based_for.md

@@ -2,39 +2,40 @@
 
 ## Description
 
-The range-based `FOR` statement is used to iterate over a range of numeric values. The iteration is performed in
-increasing order when used with `TO` clause and in decreasing order when used with `DOWNTO` clause.
+The range-based `FOR` statement iterates over a range of numeric values. The iteration is performed in
+increasing order with the `TO` clause, or in decreasing order with the `DOWNTO` clause.
 
 ## Syntax
 
 ```
 [<label> :]
-FOR <variable> = <initial value> {TO | DOWNTO} <final value> [BY <by value>] DO
-    <statement>
+FOR <variable> = <initial value> {TO | DOWNTO} <final value> [BY <step value>] DO
+    <compound statement>
 ```
 
 ## Notes
 
-- If omitted, `<by value>` is `1`.
+- If omitted, `<step value>` is `1`.
 - `<variable>` also accepts parameters.
-- `<variable>`, `<initial value>`, `<final value>` and `<by value>` must be expressions of exact numeric types.
-- `BREAK` or `LEAVE [<label>]` can be used to exit the loop.
-- `CONTINUE [<label>]` can be used to restart the next loop iteration.
-- `<variable>` can be assigned by user code inside the loop.
+- `<variable>`, `<initial value>`, `<final value>` and `<step value>` must be expressions of exact numeric types.
+- `BREAK` or `LEAVE [<label>]` exits the loop.
+- `CONTINUE [<label>]` skips the remainder of the loop body and starts the next iteration.
+- `<variable>` can be modified by the loop body.
 
 ## Execution
 
-- `<initial value>` is evaluated and assigned to `<variable>`. If it is `NULL`, the loop is not executed.
-- `<final value>` is evaluated and assigned to a temporary variable. If it is `NULL`, the loop is not executed.
-- `<by value>` (or its default `1` value) is evaluated and assigned to a temporary variable.
-  If it is `NULL`, the loop is not executed. If it is zero or negative, an error is raised.
+- `<initial value>` is evaluated and assigned to `<variable>`. If `NULL`, the loop exits immediately.
+- `<final value>` is evaluated and assigned to a temporary variable. If `NULL`, the loop exits immediately.
+- `<step value>` (or its default value `1`) is evaluated and assigned to a temporary variable.
+  If `NULL`, the loop exits immediately. If zero or negative, an error is raised.
 - Loop starts:
-  - If it is not the first iteration:
-    - If `<variable>` is `NULL`, the loop is exited.
-    - `<variable>` is incremented (`TO`) or decremented (`DOWNTO`) by the cached `<by value>`.
+  - If not the first iteration:
+    - If `<variable>` is `NULL`, the loop exits.
+    - `<variable>` is incremented (`TO`) or decremented (`DOWNTO`) by the cached `<step value>`.
   - `<variable>` is compared (less than or equal for `TO` or greater than or equal for `DOWNTO`) to the cached
-    `<final value>` and if it is out of range, the loop is exited.
-  - Loop continues to the next iteration.
+    `<final value>` and if false, the loop exits.
+  - The body (`<compund statement>`) of the loop is executed.
+  - The loop continues to the next iteration.
 
 ## Examples