New q in faq

doc/faq.wiki

@@ -34,6 +34,8 @@ Miscellaneous:
 
  [#xorriso_aliases  What personalities are supported by xorriso ?]
 
+ [#xorriso_dialog_mode  What is xorriso dialog mode useful for ?]
+
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 '''Burning'''
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@@ -160,6 +162,9 @@ Further there are calls for library startup and shutdown, for problem
 handling, and for the interpreters of xorriso's command line interface.
 The xorriso API encapsulates calls to libisofs, libburn, and libisoburn.
 
+An alternative to the xorriso C API is xorriso dialog mode.
+[#xorriso_dialog_mode See below.]
+
 The known existing GUIs [http://www.xfce.org/projects/xfburn/ Xfburn],
 [http://projects.gnome.org/brasero/ Brasero],
 [http://flburn.sourceforge.net/ FlBurn]
@@ -196,6 +201,20 @@ osirrox allows to copy files from ISO image to disk and to apply option -mount
 to one or more of the existing ISO sessions. This is normally enabled by
 option -osirrox "on:o_excl_off".
 
+===== What is xorriso dialog mode useful for ? ===== #xorriso_dialog_mode
+
+Dialog mode is initiated if -dialog "on" is among the program arguments.
+It can be used to inspect and exploit existing ISO 9660 images or
+to explore xorriso's behavior in order to develop the command sequence
+for a batch run.
+
+Frontend programmers may fork xorriso initiating a xorriso dialog session
+(-dialog "on" -use_readline "off" -pkt_output "on" -mark "done"),
+and interact with it from their own program via pipes connected to
+xorriso's stdin and stdout. This is more efficient than forking xorriso
+every now and then to perform various commands in order to complete
+complex tasks like image size prediction.
+
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