Update style guide.

PiperOrigin-RevId: 559743120
Change-Id: I6073911526bef9a9cc72d95122c4e8b9993b22ba

STYLEGUIDE.md

@@ -34,7 +34,7 @@ takes precedence. Additional principles include:
 
 - Follow the [naming conventions](https://mujoco.readthedocs.io/en/latest/programming#naming-convention).
 - Be sparing with horizontal space: Try to keep lines short, avoid line-breaks
-where possble.
+  where possible.
 - Be generous with vertical space: Empty lines between code blocks are good.
 - Keep names short.
 - Inline comments are part of the code, treat them as such.
@@ -59,7 +59,7 @@ spot such a pattern, feel free to send a PR to update the guide.
 Line length is 100 characters. In rare situations, like the collision table at
 the top of
 [engine_collision_driver.c](https://github.com/deepmind/mujoco/blob/c8ff7b3d341560e8cc33fbdcaffbcdbc4c32327c/src/engine/engine_collision_driver.c#L36),
-longer lines are alowed for readability.
+longer lines are allowed for readability.
 
 #### Comments
 
@@ -88,8 +88,8 @@ including for one-line blocks:
   ```C
   // transpose matrix
   void mju_transpose(mjtNum* res, const mjtNum* mat, int nr, int nc) {
-    for (int i=0; i<nr; i++) {
-      for (int j=0; j<nc; j++) {
+    for (int i=0; i < nr; i++) {
+      for (int j=0; j < nc; j++) {
         res[j*nr+i] = mat[i*nc+j];
       }
     }
@@ -108,7 +108,7 @@ before the `else`:
   // rotate vector by quaternion
   void mju_rotVecQuat(mjtNum res[3], const mjtNum vec[3], const mjtNum quat[4]) {
     // null quat: copy vec
-    if (quat[0]==1 && quat[1]==0 && quat[2]==0 && quat[3]==0) {
+    if (quat[0] == 1 && quat[1] == 0 && quat[2] == 0 && quat[3] == 0) {
       mju_copy3(res, vec);
     }
 
@@ -138,11 +138,13 @@ assignments:
   }
   ```
 
-- Spaces are not allowed around comparison operators in `for` statements and
-inside array subscripts `[]`. For an example, inspect the `mju_transpose`
-implementation above.
+- Spaces are required around comparison operators.
 
-- Three empty lines between function declarations.
+- Spaces are not allowed around operators in array subscripts `[]` or in
+  variable initialisation in `for` loops. For example, inspect the
+  `mju_transpose` implementation above.
+
+- Three blank lines are required between function implementations in source files.
 
 #### Variable declarations