text: Improve text protocol documentation

Add some missing descriptions to the text protocol file.

protocol/text.xml

@@ -40,7 +40,7 @@
     <request name="set_surrounding_text">
       <description summary="sets the surrounding text">
         Sets the plain surrounding text around the input position. Cursor is the
-        position within the surrounding text. Anchor is the position of the
+        byte index within the surrounding text. Anchor is the byte index of the
         selection anchor within the surrounding text. If there is no selected
 	text anchor is the same as cursor.
       </description>
@@ -68,6 +68,11 @@
       <arg name="seat" type="object" interface="wl_seat"/>
     </request>
     <request name="reset">
+      <description summary="reset">
+        Should be called by an editor widget when the input state should
+        be reseted, for example after the text was changed outside of the
+        normal input method flow.
+      </description>
      </request>
     <request name="set_micro_focus">
       <arg name="x" type="int"/>
@@ -79,19 +84,43 @@
     <request name="set_content_type"/>
 
     <event name="commit_string">
+      <description summary="commit">
+        Notify when text should be inserted into the editor widget. The text
+        to commit could be either just a single character after a key press
+        or the result of some composing (pre-edit). It also sets the new
+        cursor position (as byte index) relative to the inserted text.
+      </description>
       <arg name="text" type="string"/>
       <arg name="index" type="uint"/>
     </event>
     <event name="preedit_string">
+      <description summary="pre-edit">
+        Notify when a new composing text (pre-edit) should be set around the
+        current cursor position. Any previously set composing text should
+        be removed. It also sets the cursor positon (as byte index) relative
+        to the start of the composing text.
+      </description>
       <arg name="text" type="string"/>
       <arg name="index" type="uint"/>
     </event>
     <event name="delete_surrounding_text">
+      <description summary="delete surrounding text">
+        Notify when the text around the current cursor position should be
+        deleted. Index is relative to the current cursor (as byte index).
+        Length is the length of deleted text (as bytes).
+      </description>
       <arg name="index" type="int"/>
       <arg name="length" type="uint"/>
     </event>
     <event name="preedit_styling"/>
     <event name="key">
+      <description summary="key">
+        Notify when a key event was sent. Key events should not be used
+        for normal text input operations, which should be done with
+        commit_string, delete_surrounfing_text, etc. The key event follows
+        the wl_keyboard key event convention. Key is a XKB keycode, state a
+        wl_keyboard key_state.
+      </description>
       <arg name="key" type="uint"/>
       <arg name="state" type="uint"/>
     </event>