Update README

README.md

@@ -99,13 +99,13 @@ Rendering app into DOM and animate it.
 
 Controlling the aesthetic appearance of the shapes.
 
-- [app.**scene**](#app-scene)
-- [app.**background**](#app-background)
-- [app.**stroke**](#app-stroke)
-- [app.**noStroke**](#app-nostroke) - Disables drawing the stroke of shapes.
-- [app.**fill**](#app-fill)
-- [app.**noFill**](#app-nofill) - Disables drawing the fill of shapes.
-- [cm.**wide**](#cm-wide)
+- [app.**scene**](#app-scene) - Sets the specified css _color_ used for the background of the rendering context of the app and returns this app.
+- [app.**background**](#app-background) - Sets the specified color (_ch_, _fg_, _bg_) used for the background of the app in cells and returns this app.
+- [app.**stroke**](#app-stroke) - Sets the specified color (_ch_, _fg_, _bg_) for drawing the stroke of shapes and returns this app.
+- [app.**noStroke**](#app-nostroke) - Disables drawing the stroke of shapes and returns this app.
+- [app.**fill**](#app-fill) - Sets the specified color (_ch_, _fg_, _bg_) for drawing the fill of shapes and returns this app.
+- [app.**noFill**](#app-nofill) - Disables drawing the fill of shapes and returns this app.
+- [cm.**wide**](#cm-wide) - Marks the _ch_ as a wide character and returns the marked code point of it.
 
 ### [Drawing Shapes](#drawing-shapes-1)
 
@@ -198,21 +198,23 @@ app.stop();
 
 <a name="app-scene" href="#app-scene">#</a> app.**scene**(_color_)
 
+Sets the specified css _color_ used for the background of the rendering context of the app and returns this app. For example, to render a light theme app:
+
 ```js
-app.scene("#000000");
+app.scene("#aaaaaa");
 ```
 
 <a name="app-background" href="#app-background">#</a> app.**background**(_ch[, fg[, bg]]_)
 
-Sets the specified color used for the background of the app.
+Sets the specified color (_ch_, _fg_, _bg_) used for the background of the app in cells and returns this app. For example, to color every cells with `("·", "steelblue", "orange")`:
 
 ```js
 app.background("·", "steelblue", "orange");
 ```
 
 <a name="app-stroke" href="#app-stroke">#</a> app.**stroke**(_ch[, fg[, bg]]_)
 
-Sets the specified color (_ch_, _fg_, _bg_) for drawing the stroke of shapes. Calling _app_.stroke means all the shapes drawn after that will be stroked with the specified color. For example, to draw a [point](#app-point) and a [line](#app-line) with the same stroke:
+Sets the specified color (_ch_, _fg_, _bg_) for drawing the stroke of shapes and returns this app. Calling _app_.stroke means all the shapes drawn after that will be stroked with the specified color. For example, to draw a [point](#app-point) and a [line](#app-line) with the same stroke:
 
 ```js
 app.stroke("@", "steelblue", "orange");
@@ -222,7 +224,7 @@ app.line(0, 0, 10, 10);
 
 <a name="app-nostroke" href="#app-nostroke">#</a> app.**noStroke**()
 
-Disables drawing the stroke of shapes. For example, to draw a only filled [rectangle](#app-rect):
+Disables drawing the stroke of shapes and returns this app. For example, to draw a only filled [rectangle](#app-rect):
 
 ```js
 app.noStroke();
@@ -232,7 +234,7 @@ app.rect(0, 0, 5, 5);
 
 <a name="app-fill" href="#app-fill">#</a> app.**fill**(_ch[, fg[, bg]]_)
 
-Sets the specified color (_ch_, _fg_, _bg_) for drawing the fill of shapes. Calling _app_.fill means all the shapes drawn after that will be filled with the specified color. For example, to draw two filled [rectangles](#app-rect) with the same fill:
+Sets the specified color (_ch_, _fg_, _bg_) for drawing the fill of shapes and returns this app. Calling _app_.fill means all the shapes drawn after that will be filled with the specified color. For example, to draw two filled [rectangles](#app-rect) with the same fill:
 
 ```js
 app.fill("@", "steelblue", "orange");
@@ -242,7 +244,7 @@ app.rect(6, 6, 3, 3);
 
 <a name="app-nofill" href="#app-nofill">#</a> app.**noFill**()
 
-Disables drawing the fill of shapes. For example, to draw only stroked [rectangle](#app-rect):
+Disables drawing the fill of shapes and returns this app. For example, to draw only stroked [rectangle](#app-rect):
 
 ```js
 app.noFill();
@@ -252,8 +254,16 @@ app.rect(0, 0, 5, 5);
 
 <a name="cm-wide" href="#cm-wide">#</a> cm.**wide**(_ch_)
 
+Marks the _ch_ as a wide character and returns the marked code point of it. In double mode, a wide character draws once to fill a cell, and a normal character draws twice to fill a cell. For example, to draw two [lines](#app-line) stroked with different characters but with equal length:
+
 ```js
-cm.wide("🚀");
+const app = await cm.app({ mode: "double" });
+
+app.stroke(cm.wide("🚀"));
+app.line(0, 0, 10, 0);
+
+app.stoke("@");
+app.line(0, 2, 10, 2);
 ```
 
 ## Drawing Shapes