[gtk/attribute-docs] entry: Document buildable support

[Matthias Clasen <matthiasc src gnome org>]

commit 12b97ffd24e35ea45f6d4a5c78b1b0e10965c4ac
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Apr 6 23:29:47 2020 -0400

    entry: Document buildable support

 gtk/gtkentry.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
---
diff --git a/gtk/gtkentry.c b/gtk/gtkentry.c
index e823ab0d08..5e95bd6fc3 100644
--- a/gtk/gtkentry.c
+++ b/gtk/gtkentry.c
@@ -138,6 +138,30 @@
  *
  * For all the subnodes added to the text node in various situations,
  * see #GtkText.
+ *
+ * # GtkEntry as GtkBuildable
+ *
+ * The GtkEntry implementation of the GtkBuildable interface supports a
+ * custom <attributes> element, which supports any number of <attribute>
+ * elements. The <attribute> element has attributes named “name“, “value“,
+ * “start“ and “end“ and allows you to specify #PangoAttribute values for
+ * this label.
+ *
+ * An example of a UI definition fragment specifying Pango attributes:
+ * |[
+ * <object class="GtkEnry">
+ *   <attributes>
+ *     <attribute name="weight" value="PANGO_WEIGHT_BOLD"/>
+ *     <attribute name="background" value="red" start="5" end="10"/>
+ *   </attributes>
+ * </object>
+ * ]|
+ *
+ * The start and end attributes specify the range of characters to which the
+ * Pango attribute applies. If start and end are not specified, the attribute is
+ * applied to the whole text. Note that specifying ranges does not make much
+ * sense with translatable attributes. Use markup embedded in the translatable
+ * content instead.
  */
 
 #define MAX_ICONS 2