+/** \addtogroup XBT_log
+ *
+ * This section describes the API to the log functions used
+ * everywhere in this project.
+
+\section log_overview Overview
+
+This is an adaptation of the log4c project, which is dead upstream, and
+which I was given the permission to fork under the LGPL licence by the
+authors. log4c itself was loosely based on the Apache project's Log4J,
+Log4CC, etc. project. Because C is not object oriented, a lot had to change.
+
+There is 3 main concepts: category, priority and appender. These three
+concepts work together to enable developers to log messages according to
+message type and priority, and to control at runtime how these messages are
+formatted and where they are reported.
+
+\section log_cat Category hierarchy
+
+The first and foremost advantage of any logging API over plain printf()
+resides in its ability to disable certain log statements while allowing
+others to print unhindered. This capability assumes that the logging space,
+that is, the space of all possible logging statements, is categorized
+according to some developer-chosen criteria.
+
+This observation led to choosing category as the central concept of the
+system. Every category is declared by providing a name and an optional
+parent. If no parent is explicitly named, the root category, LOG_ROOT_CAT is
+the category's parent.
+
+A category is created by a macro call at the top level of a file. A
+category can be created with any one of the following macros:
+
+ - \ref XBT_LOG_NEW_CATEGORY(MyCat); Create a new root
+ - \ref XBT_LOG_NEW_SUBCATEGORY(MyCat, ParentCat);
+ Create a new category being child of the category ParentCat
+ - \ref XBT_LOG_NEW_DEFAULT_CATEGORY(MyCat);
+ Like XBT_LOG_NEW_CATEGORY, but the new category is the default one
+ in this file
+ - \ref XBT_LOG_NEW_DEFAULT_SUBCATEGORY(MyCat, ParentCat);
+ Like XBT_LOG_NEW_SUBCATEGORY, but the new category is the default one
+ in this file
+
+The parent cat can be defined in the same file or in another file (in
+which case you want to use the \ref XBT_LOG_EXTERNAL_CATEGORY macro to make
+it visible in the current file), but each category may have only one
+definition.
+
+Typically, there will be a Category for each module and sub-module, so you
+can independently control logging for each module.
+
+For a list of all existing categories, please refer to the \ref XBT_log_cats section.
+
+\section log_pri Priority
+
+A category may be assigned a threshold priorty. The set of priorites are
+defined by the \ref e_xbt_log_priority_t enum. All logging request under
+this priority will be discarded.
+
+If a given category is not assigned a threshold priority, then it inherits
+one from its closest ancestor with an assigned threshold. To ensure that all
+categories can eventually inherit a threshold, the root category always has
+an assigned threshold priority.
+
+Logging requests are made by invoking a logging macro on a category. All of
+the macros have a printf-style format string followed by arguments. If you
+compile with the -Wall option, gcc will warn you for unmatched arguments, ie
+when you pass a pointer to a string where an integer was specified by the
+format. This is usualy a good idea.
+
+Because most C compilers do not support vararg macros, there is a version of
+the macro for any number of arguments from 0 to 6. The macro name ends with
+the total number of arguments.
+
+Here is an example of the most basic type of macro. This is a logging
+request with priority <i>warning</i>.
+
+<code>CLOG5(MyCat, gras_log_priority_warning, "Values are: %d and '%s'", 5,
+"oops");</code>
+
+A logging request is said to be enabled if its priority is higher than or
+equal to the threshold priority of its category. Otherwise, the request is
+said to be disabled. A category without an assigned priority will inherit
+one from the hierarchy.
+
+It is possible to use any non-negative integer as a priority. If, as in the
+example, one of the standard priorites is used, then there is a convenience
+macro that is typically used instead. For example, the above example is
+equivalent to the shorter:
+
+<code>CWARN4(MyCat, "Values are: %d and '%s'", 5, "oops");</code>
+
+\subsection log_subcat Using a default category
+
+If \ref XBT_LOG_NEW_DEFAULT_SUBCATEGORY(MyCat, Parent) or
+\ref XBT_LOG_NEW_DEFAULT_CATEGORY(MyCat) is used to create the
+category, then the even shorter form can be used:
+
+<code>WARN3("Values are: %d and '%s'", 5, "oops");</code>