Improve documentation for StyleBox.

I want to just say that the terms used by style boxes are all over the place and quite confusing.
It's even worse internally.

doc/classes/StyleBox.xml

@@ -39,7 +39,8 @@
 			<argument index="0" name="margin" type="int" enum="Margin">
 			</argument>
 			<description>
-				Return the offset of margin "margin" (see MARGIN_* enum).
+				Return the content margin offset for the specified margin
+				Positive values reduce size inwards, unlike [Control]'s margin values.
 			</description>
 		</method>
 		<method name="get_minimum_size" qualifiers="const">
@@ -70,12 +71,22 @@
 	</methods>
 	<members>
 		<member name="content_margin_bottom" type="float" setter="set_default_margin" getter="get_default_margin">
+			The bottom margin for the contents of this style box. Increasing this value reduces the space available to the contents from the bottom.
+			If this value is negative, it is ignored and a child-specific margin is used instead. For example for [StyleBoxFlat] the border thickness (if any) is used instead.
+			It is up to the code using this style box to decide what these contents are: for example, a [Button] respects this content margin for the textual contents of the button.
+			[method get_margin] should be used to fetch this value as consumer instead of reading these properties directly. This is because it correctly respects negative values and the fallback mentioned above.
 		</member>
 		<member name="content_margin_left" type="float" setter="set_default_margin" getter="get_default_margin">
+			The left margin for the contents of this style box.	Increasing this value reduces the space available to the contents from the left.
+			Refer to [member content_margin_bottom] for extra considerations.
 		</member>
 		<member name="content_margin_right" type="float" setter="set_default_margin" getter="get_default_margin">
+			The right margin for the contents of this style box. Increasing this value reduces the space available to the contents from the right.
+			Refer to [member content_margin_bottom] for extra considerations.
 		</member>
 		<member name="content_margin_top" type="float" setter="set_default_margin" getter="get_default_margin">
+			The top margin for the contents of this style box. Increasing this value reduces the space available to the contents from the top.
+			Refer to [member content_margin_bottom] for extra considerations.
 		</member>
 	</members>
 	<constants>

doc/classes/StyleBoxTexture.xml

@@ -42,28 +42,49 @@
 		<member name="draw_center" type="bool" setter="set_draw_center" getter="is_draw_center_enabled">
 		</member>
 		<member name="expand_margin_bottom" type="float" setter="set_expand_margin_size" getter="get_expand_margin_size">
+			Expands the bottom margin of this style box when drawing, causing it be drawn larger than requested.
 		</member>
 		<member name="expand_margin_left" type="float" setter="set_expand_margin_size" getter="get_expand_margin_size">
+			Expands the left margin of this style box when drawing, causing it be drawn larger than requested.
 		</member>
 		<member name="expand_margin_right" type="float" setter="set_expand_margin_size" getter="get_expand_margin_size">
+			Expands the right margin of this style box when drawing, causing it be drawn larger than requested.
 		</member>
 		<member name="expand_margin_top" type="float" setter="set_expand_margin_size" getter="get_expand_margin_size">
+			Expands the top margin of this style box when drawing, causing it be drawn larger than requested.
 		</member>
 		<member name="margin_bottom" type="float" setter="set_margin_size" getter="get_margin_size">
+			Increases the bottom margin of the 3x3 texture box.
+			A higher value means more of the source texture is considered to be part of the bottom border of the 3x3 box.
+			This is also the value used as fallback for [member StyleBox.content_margin_bottom] if it is negative.
 		</member>
 		<member name="margin_left" type="float" setter="set_margin_size" getter="get_margin_size">
+			Increases the left margin of the 3x3 texture box.
+			A higher value means more of the source texture is considered to be part of the left border of the 3x3 box.
+			This is also the value used as fallback for [member StyleBox.content_margin_left] if it is negative.
 		</member>
 		<member name="margin_right" type="float" setter="set_margin_size" getter="get_margin_size">
+			Increases the right margin of the 3x3 texture box.
+			A higher value means more of the source texture is considered to be part of the right border of the 3x3 box.
+			This is also the value used as fallback for [member StyleBox.content_margin_right] if it is negative.
 		</member>
 		<member name="margin_top" type="float" setter="set_margin_size" getter="get_margin_size">
+			Increases the top margin of the 3x3 texture box.
+			A higher value means more of the source texture is considered to be part of the top border of the 3x3 box.
+			This is also the value used as fallback for [member StyleBox.content_margin_top] if it is negative.
 		</member>
 		<member name="modulate_color" type="Color" setter="set_modulate" getter="get_modulate">
+			Modulates the color of the texture when this style box is drawn.
 		</member>
 		<member name="normal_map" type="Texture" setter="set_normal_map" getter="get_normal_map">
+			The normal map to use when drawing this style box.
 		</member>
 		<member name="region_rect" type="Rect2" setter="set_region_rect" getter="get_region_rect">
+			Species a sub region of the texture to use.
+			This is equivalent to first wrapping the texture in an [AtlasTexture] with the same region.
 		</member>
 		<member name="texture" type="Texture" setter="set_texture" getter="get_texture">
+			The texture to use when drawing this style box.
 		</member>
 	</members>
 	<signals>