Small corrections to writing-marble-tests.md (#2967)

doc/writing-marble-tests.md

@@ -26,7 +26,7 @@ The unit tests have helper methods that have been added to make creating tests e
 
 ### Ergonomic defaults for `hot` and `cold`
 
-In both `hot` and `cold` methods, value charecters specified in marble diagrams are emitted as strings unless a `values`
+In both `hot` and `cold` methods, value characters specified in marble diagrams are emitted as strings unless a `values`
 argument is passed to the method. Therefor:
 
 `hot('--a--b')` will emit `"a"` and `"b"` whereas
@@ -43,13 +43,14 @@ Likewise, unspecified errors will just default to the string `"error"`, so:
 ## Marble Syntax
 
 Marble syntax is a string which represents events happening over "time". The first character of any marble string
+
 always represents the "zero frame". A "frame" is somewhat analogous to a virtual millisecond.
 
 - `"-"` time: 10 "frames" of time passage.
 - `"|"` complete: The successful completion of an observable. This is the observable producer signaling `complete()`
 - `"#"` error: An error terminating the observable. This is the observable producer signaling `error()`
-- `"a"` any character: All other characters represent a value being emitted by the producure signaling `next()`
-- `"()"` sync groupings: When multiple events need to single in the same frame synchronously, parenthesis are used
+- `"a"` any character: All other characters represent a value being emitted by the producer signaling `next()`
+- `"()"` sync groupings: When multiple events need to be in the same frame synchronously, parentheses are used
  to group those events. You can group nexted values, a completion or an error in this manner. The position of the 
  initial `(` determines the time at which its values are emitted.
 - `"^"` subscription point: (hot observables only) shows the point at which the tested observables will be subscribed
@@ -71,7 +72,7 @@ always represents the "zero frame". A "frame" is somewhat analogous to a virtual
 
 `'-a-^-b--|'`: In a hot observable, on frame -20 emit `a`, then on frame 20 emit `b`, and on frame 50, `complete`.
 
-`'--(abc)-|'`: on frame 20, emit `a`, `b`, and `c`, then on frame 80 `complete`
+`'--(abc)-|'`: on frame 20, emit `a`, `b`, and `c`, then on frame 30 `complete`
 
 `'-----(a|)'`: on frame 50, emit `a` and `complete`.
 
@@ -154,7 +155,7 @@ expectSubscriptions(y.subscriptions).toBe(ysubs);
 - Align the start of `xsubs` and `ysubs` diagrams with `expected` diagram.
 - Notice how the `x` cold observable is unsubscribed at the same time `e1` emits `y`.
 
-In most tests it will be unnecessary to test subscription and unsubscription points, be either obvious or can be implied from the `expected` diagram. In those cases do not write subscription assertions. In test cases that have inner subscriptions or cold observables with multiple subscribers, these subscription assertions can be useful.
+In most tests it will be unnecessary to test subscription and unsubscription points, being either obvious or implied from the `expected` diagram. In those cases do not write subscription assertions. In test cases that have inner subscriptions or cold observables with multiple subscribers, these subscription assertions can be useful.
 
 ## Generating PNG marble diagrams from tests