[gimp-help] Fix #254: Alpha channel example is wrong.

[Jacob Boerema <jboerema src gnome org>]

commit e3b939f39a074666f5786fe62183bcd2e3e06840
Author: Jacob Boerema <jgboerema gmail com>
Date:   Sun Mar 20 18:57:41 2022 -0400

    Fix #254: Alpha channel example is wrong.
    
    Fixed the problems mentioned in the issue, and adjusted text in a few
    more places.

 src/concepts/layers.xml | 101 +++++++++++++++++++++++-------------------------
 1 file changed, 48 insertions(+), 53 deletions(-)
---
diff --git a/src/concepts/layers.xml b/src/concepts/layers.xml
index 616edae9b..a7227c45b 100644
--- a/src/concepts/layers.xml
+++ b/src/concepts/layers.xml
@@ -39,20 +39,17 @@
     </mediaobject>
   </figure>
   <para>
-    There is no limit, in principle, to the number of layers an image can 
-    have: only the amount of memory available on the system. It is not 
-    uncommon for advanced users to work with images containing dozens of 
-    layers. You can group layers to make your work easier, and you have many 
-    commands to handle layers.
+    There is no limit to the number of layers an image can have, only the
+    amount of memory available on the system. It is not uncommon for advanced
+    users to work with images containing dozens of layers. You can group layers
+    to make your work easier, and there are many commands to handle layers.
   </para>
   <para>
-    The organization of layers in an image is shown by the Layers dialog,
+    The organization of layers in an image is shown in the Layers dialog,
     which is the second most important type of dialog window in
-    <acronym>GIMP</acronym>, after
-    the Main Toolbox. The appearance of the Layers dialog is shown in the
-    adjoining illustration. How it works is described in detail in the
-    <link linkend="gimp-layer-dialog">Layers Dialog</link>
-    section, but we will touch on some aspects of it here, in relation to the
+    <acronym>GIMP</acronym>, after the Main Toolbox. How it works is described
+    in detail in the <link linkend="gimp-layer-dialog">Layers Dialog</link>
+    section, but we will touch some aspects of it here, in relation to the
     layer properties that they display.
   </para>
   <para>
@@ -60,20 +57,18 @@
     Each open image has at any time a single
     <emphasis>active drawable</emphasis>. A <quote>drawable</quote>
     is a <acronym>GIMP</acronym> concept that includes layers, but also
-    several other types of
-    things, such as channels, layer masks, and the selection mask. (Basically,
-    a <quote>drawable</quote>
-    is anything that can be drawn on with painting tools). If a layer is
-    currently active, it is shown highlighted in the Layers dialog, and its
-    name is shown in the status area of the image window. If not, you can
-    activate it by clicking on it. If none of the layers are highlighted, it
-    means the active drawable is something other than a layer.
+    several other items, such as channels, layer masks, and the selection mask.
+    Basically, a <quote>drawable</quote> is anything that can be drawn on with
+    painting tools. If a layer is currently active, it is shown highlighted in
+    the Layers dialog, and its name is shown in the status area of the image
+    window. If not, you can activate it by clicking on it. If none of the
+    layers are highlighted, it means the active drawable is something else than
+    a layer.
   </para>
   <para>
-    In the menu bar above an image window, you can find a menu called
-    <guimenu>Layer</guimenu>, containing a number of commands that
-    affect the active layer of the image.  The same menu can be
-    accessed by right-clicking in the Layers dialog.
+    In the menu bar, you can find a menu called <guimenu>Layer</guimenu>,
+    containing a number of commands that affect the active layer of the image.
+    The same menu can be accessed by right-clicking in the Layers dialog.
   </para>
 
   <sect2 id="gimp-layer-properties">
@@ -91,7 +86,7 @@
             Every layer has a name. This is assigned automatically when the
             layer is created, but you can change it. You can change the name
             of a layer either by double-clicking on it in the Layers dialog,
-            or by right-clicking there and then selecting the top entry in the
+            or by right-clicking there, and then selecting the top entry in the
             menu that appears,
             <guimenuitem>Edit Layer Attributes</guimenuitem>.
           </para>
@@ -115,21 +110,22 @@
             are partial transparencies.
           </para>
           <para>
-            The <emphasis>background layer</emphasis> is particular. If you 
-            have just created a new image, it has still only one layer which 
-            is a background layer. If the image has been created with an 
-            opaque Fill type, this one layer has no Alpha channel. To get a 
-            background layer with transparency, either you create your new 
-            image with a transparent Fill type, or you use the
-            <link linkend="gimp-layer-alpha-add">Add an Alpha Channel</link>. 
+            The <emphasis>background layer</emphasis> is special. If you
+            have just created a new image, it only has one layer, which
+            is the background layer. If the image has been created with an
+            opaque Fill type, this one layer has no Alpha channel. To get a
+            background layer with transparency, either create your new image
+            with a transparent Fill type, or you use the
+            <link linkend="gimp-layer-alpha-add">Add an Alpha Channel</link>
+            command.
           </para>
           <para>
-            If you add a <emphasis>new layer</emphasis>, even with an opaque Fill 
-            type, an Alpha channel is automatically added to the layer. 
+            If you add a <emphasis>new layer</emphasis>, even with an opaque Fill
+            type, an Alpha channel is automatically added to the layer.
           </para>
           <para>
-            Every layer other than the bottom layer of an image has
-            automatically an Alpha channel, but you can't see a grayscale
+            Every layer other than the bottom layer of an image automatically
+            has an Alpha channel, but you can't see a grayscale
             representation of the alpha values. See
             <link linkend="glossary-alpha">Alpha</link> in Glossary for
             more information.
@@ -153,7 +149,7 @@
                       Red, Green, and Blue. In the Channel Dialog, you can see
                       that an alpha Channel has been added. It is white because
                       the image is not transparent since there is at least one
-                      100% opaque layer. The current layer is the red one : since
+                      100% opaque layer. The current layer is the red one: since
                       it is painted with pure red, there is no green and no blue
                       and the corresponding channels are black.
                     </para>
@@ -203,12 +199,11 @@
                   </imageobject>
                   <caption>
                     <para>
-                      The left part of the third layer has been made 
-                      transparent. The Alpha channel is still white and the 
-                      left part of the layer is opaque. The background layer 
-                      has no Alpha channel. In this case, the Clear command 
-                      works like the Eraser and uses the Background color of 
-                      Toolbox.
+                      The left part of the third layer has been cleared. The
+                      Alpha channel is still white and the left part of the
+                      layer is opaque, because the background layer has no
+                      Alpha channel. In this case, the Clear command works like
+                      the Eraser and uses the Background color of Toolbox.
                     </para>
                   </caption>
                 </mediaobject>
@@ -232,7 +227,7 @@
                       </menuchoice>
                       command, on the Background layer.
                       Now, the left part of the image is fully transparent and
-                      has the color of the page the image is lying on. The left
+                      has the color of the page where the image is shown. The left
                       part of the Alpha Channel thumbnail is black (transparent)
                       in the Channel Dialog.
                     </para>
@@ -253,7 +248,7 @@
           </indexterm>
           <para>
             The layer type is determined by the image type (see previous
-            section) and the presence or absence of an alpha channel. These
+            section), and the presence or absence of an alpha channel. These
             are the possible layer types:
           </para>
           <itemizedlist>
@@ -265,12 +260,12 @@
             <listitem><para>IndexedA</para></listitem>
           </itemizedlist>
           <para>
-            The main reason this matters is that most filters (in the
-            <guimenu>Filters</guimenu>
-            menu) only accept a subset of layer types, and appear grayed out
-            in the menu if the active layer does not have an acceptable type.
+            The main reason this matters is that some filters (in the
+            <guimenu>Filters</guimenu> menu) only accept a subset of layer
+            types, and appear disabled in the menu if the active layer does
+            not have a supported type.
             Often you can rectify this either by changing the mode of the
-            image or by adding or removing an alpha channel.
+            image, or by adding or removing an alpha channel.
           </para>
         </listitem>
       </varlistentry>
@@ -388,10 +383,10 @@
           </indexterm>
           <para>
             In <acronym>GIMP</acronym>, the boundaries of a layer do not
-            necessarily match the
-            boundaries of the image that contains it. When you create text,
-            for example, each text item goes into its own separate layer, and
-            the layer is precisely sized to contain the text and nothing more.
+            necessarily match the boundaries of the image that contains it.
+            When you create text, for example, each text item belongs to its
+            own separate layer, and the layer size is automatically adjusted to
+            contain the text and nothing more.
             Also, when you create a new layer using cut-and-paste, the new
             layer is sized just large enough to contain the pasted item. In
             the image window, the boundaries of the currently active layer are