chore(api): Incorporate hints from Hamish about Exceptions

files/en-us/web/api/canvasrenderingcontext2d/arcto/index.md

@@ -8,15 +8,12 @@ browser-compat: api.CanvasRenderingContext2D.arcTo
 
 {{APIRef}}
 
-The
-**`CanvasRenderingContext2D.arcTo()`**
-method of the Canvas 2D API adds a circular arc to the current sub-path, using the given
-control points and radius. The arc is automatically connected to the path's latest point
-with a straight line, if necessary for the specified parameters.
+The **`CanvasRenderingContext2D.arcTo()`** method of the Canvas 2D API adds a circular arc to the current sub-path, using the given control points and radius.
+The arc is automatically connected to the path's latest point with a straight line if necessary, for example if the control points are in a line.
 
 This method is commonly used for making rounded corners.
 
-> **Note:** Be aware that you may get unexpected results when using a
+> **Note:** You may get unexpected results when using a
 > relatively large radius: the arc's connecting line will go in whatever direction it
 > must to meet the specified radius.
 
@@ -43,31 +40,11 @@ arcTo(x1, y1, x2, y2, radius)
 
 None ({{jsxref("undefined")}}).
 
-### Usage notes
+### Exceptions
 
-There are some special cases to consider when describing the action of
-`arcTo()`. Let <em>P<sub>0</sub></em> be the current point on the path when
-`arcTo()` is called, <em>P<sub>1</sub></em> = (x1, y1), and
-<em>P<sub>2</sub></em> = (x2, y2) be the first and second control points
-respectively, and _r_ = radius be the `radius` specified in the call.
+- `IndexSizeError` {{domxref("DOMException")}}
 
-- If _r_ is negative, it is an error, and an `IndexSizeError` [DOMException](/en-US/docs/Web/API/DOMException) is raised.
-
-- If _r_ is 0, `arcTo()` behaves as if <em>P<sub>0</sub></em>,
-  <em>P<sub>1</sub></em>, and <em>P<sub>2</sub></em> are collinear (in a line).
-
-- In the case of all of the points being collinear, a line from
-  <em>P<sub>0</sub></em> to <em>P<sub>1</sub></em> is drawn
-  unless the points <em>P<sub>0</sub></em> and <em>P<sub>1</sub></em> are
-  coincident (on top of each other), in which case nothing is drawn.
-
-For the usual case of _r_ being positive and <em>P<sub>0</sub></em>,
-<em>P<sub>1</sub></em>, and <em>P<sub>2</sub></em> not being collinear,
-drawing always consists of an arc and possibly a line connecting the current
-position on the path to that arc.
-To visualize how this works, an interactive demo shows the
-construction of the path generated by `arcTo()` in
-[Construction of `arcTo()` path](#construction_of_arcto_path).
+  - : Thrown if `radius` is a negative value.
 
 ## Examples
 
@@ -207,15 +184,22 @@ ctx.stroke();
 
 {{ EmbedLiveSample('Result_of_a_large_radius', 315, 165) }}
 
-### Construction of arcTo() path
+### Constructing an arcTo() path
 
 The demo shows the semi-infinite lines and circle with center _C_ tangent
 to the lines at <em>T<sub>1</sub></em> and <em>T<sub>2</sub></em> used to
-determine the path rendered by `arcTo()`. Besides being able to set the arc radius with
-the slider, the initial point <em>P<sub>0</sub></em> and control points
-<em>P<sub>1</sub></em> and <em>P<sub>2</sub></em> can be moved by
-dragging them with the mouse with the left button down. The numeric values can also
-be edited, and the arrow keys can be used to change an underlined element that is in focus.
+determine the path rendered by `arcTo()`.
+
+Note that `arcTo` will create a straight line when <em>P<sub>1</sub></em>
+and <em>P<sub>2</sub></em> are in a line. Additionally, nothing is drawn by
+`arcTo` if <em>P<sub>1</sub></em> and <em>P<sub>2</sub></em> have the same
+coordinates.
+
+Besides being able to set the arc radius with the slider, the initial point
+<em>P<sub>0</sub></em> and control points <em>P<sub>1</sub></em> and
+<em>P<sub>2</sub></em> can be moved by dragging them with the mouse with the
+left button down. The numeric values can also be edited, and the arrow keys
+can be used to change an underlined element that is in focus.
 
 ```html hidden
 <div>
@@ -997,7 +981,7 @@ label {
 }
 ```
 
-{{ EmbedLiveSample("Construction of arcTo() path", 350, 450) }}
+{{ EmbedLiveSample("constructing_an_arcto_path", 350, 450) }}
 
 ### Animating `arcTo()` drawing
 
@@ -1072,7 +1056,7 @@ loop(0);
 
 #### Result
 
-{{EmbedLiveSample('Live_demo', 315, 200) }}
+{{EmbedLiveSample('animating_arcto_drawing', 315, 200) }}
 
 ## Specifications