If you want to mimic the simple layout with the format one, you would use this
-format: '[%%h:%%i:(%%I) %%r] %%l: [%%c/%%p] %%m%%n'. This is not completely correct
+format: '[%%h:%%i:(%%i) %%r] %%l: [%%c/%%p] %%m%%n'. This is not completely correct
because the simple layout do not display the message location for messages at
-priority INFO (thus, the fmt is '[%%h:%%i:(%%I) %%r] %%l: [%%c/%%p] %%m%%n' in this
+priority INFO (thus, the fmt is '[%%h:%%i:(%%i) %%r] [%%c/%%p] %%m%%n' in this
case). Moreover, if there is no process name (ie, messages coming from the
library itself, or test programs doing strange things) do not display the
process identity (thus, fmt is '[%%r] %%l: [%%c/%%p] %%m%%n' in that case, and '[%%r]
[%%c/%%p] %%m%%n' if they are at priority INFO).
-For now, there is only one format modifier: the precision field. You
-can for example specify %.4r to get the application age with 4
-numbers after the radix. Another limitation is that you cannot set
-specific layouts to the several priorities.
+For now, there is only two format modifiers: the precision and the
+width fields. You can for example specify %.4r to get the application
+age with 4 numbers after the radix, or %15p to get the process name
+on 15 columns. Finally, you can specify %10.6r to get the time on at
+most 10 columns, with 6 numbers after the radix.
+
+Note that when specifying the width, it is filled with spaces. That
+is to say that for example %5r in your format is converted to "% 5f"
+for printf (note the extra space); there is no way to fill the empty
+columns with 0 (ie, pass "%05f" to printf). Another limitation is
+that you cannot set specific layouts to the several priorities.
\subsection log_use_conf_app 3.1.4 Category appender
