Clarify GEN_DATA docs

docs/reference/configuration/keywords.rst

@@ -790,16 +790,21 @@ and/or history matching project.
 .. _gen_data:
 .. topic:: GEN_DATA
 
-        The ``GEN_DATA`` keyword is used to load text files which have been generated
-        by the forward model.
+        The ``GEN_DATA`` keyword is used to declare text files that are referred to by
+        :ref:`GENERAL_OBSERVATIONs <_general_observation>`. It declares
+        text files which have been generated by the forward model, which will be
+        loaded by ert when loading general observations.
+        These text files naming scheme may be arbitrary. The contents of these result files are always:
+        **exactly one number per line**. If we speak about "indexing" into a ``GEN_DATA`` file,
+        the "index" always refers to the row number, where the index 0 refers to the first row.
+        ``GEN_DATA`` will only affect the simulation if it is referred to by a
+        :ref:`GENERAL_OBSERVATION <_general_observation>`.
 
         The GEN_DATA keyword has several options, each of them required:
 
         * RESULT_FILE - This is the name of the file generated by the forward
           model and read by ERT. This filename _must_ have a %d as part of the
           name, that %d will be replaced by report step when loading.
-        * INPUT_FORMAT - The format of the file written by the forward model
-          (i.e. RESULT_FILE) and read by ERT, the only valid value is ASCII.
         * REPORT_STEPS - A list of the report step(s) where you expect the
           forward model to create a result file. I.e. if the forward model
           should create a result file for report steps 50 and 100 this setting
@@ -812,13 +817,12 @@ and/or history matching project.
 
         ::
 
-                GEN_DATA 4DWOC  INPUT_FORMAT:ASCII   RESULT_FILE:SimulatedWOC%d.txt   REPORT_STEPS:10,100
+                GEN_DATA 4DWOC   RESULT_FILE:SimulatedWOC%d.txt   REPORT_STEPS:10,100
 
         Here we introduce a GEN_DATA instance with name 4DWOC. When the forward
         model has run it should create two files with name SimulatedWOC10.txt
-        and SimulatedWOC100.txt. The result files are in ASCII format, ERT will
-        look for these files and load the content. The files should be pure
-        numbers - without any header.
+        and SimulatedWOC100.txt. For every realization, ERT will look within its storage
+        for these result files and load the content. **The files must always contain one number per line.**
 
         ERT does not have any awareness of the type of data
         encoded in a ``GEN_DATA`` keyword; it could be the result of gravimetric
@@ -831,12 +835,10 @@ and/or history matching project.
 
         ::
 
-                GEN_DATA 4DWOC  RESULT_FILE:SimulatedWOC_%d.txt  INPUT_FORMAT:ASCII   REPORT_STEPS:0
+                GEN_DATA 4DWOC  RESULT_FILE:SimulatedWOC_%d.txt   REPORT_STEPS:0
 
         The ``4DWOC`` is an arbitrary unique key, ``RESULT_FILE:SimulatedWOC%d.txt``
-        means that ERT will look for results in the file ``SimulatedWOC_0.txt``. The
-        ``INPUT_FORMAT:ASCII`` means that ERT will expect the result file to be
-        formatted as an ASCII file.
+        means that ERT will look for results in the file ``ensembles/<ensemble>/<realization>/SimulatedWOC_0.txt``.
 
         The ``REPORT_STEPS:0`` is tightly bound to the ``%d`` integer format specifier
         in the result file - at load time the ``%d`` is replaced with the integer values

docs/reference/configuration/observations.rst

@@ -124,7 +124,7 @@ The GENERAL_OBSERVATION keyword is used together with the GEN_DATA
 type. This pair of observation and data types are typically
 used when you want to update something special which does not fit into
 any of the predefined types. The ERT application just treats
-GENERAL_OBSERVATION (and also GEN_DATA) as a range of numbers with no
+GENERAL_OBSERVATION (and also GEN_DATA) as a list of numbers with no
 particular structure, this is very flexible, but of course also a bit
 more complex to use:
 
@@ -154,7 +154,9 @@ This OBS_FILE has three observations: 1.46 +/- 0.26, 25.0 +/- 5.0 and
 instance we are observing (i.e. comparing with) has the same number of
 elements as the observation, i.e. three in this case. By using the
 keyword INDEX_LIST you can select the elements of the
-GEN_DATA instance you are interested in. Consider for example:
+GEN_DATA instance you are interested in. Each index in INDEX_LIST
+points to a line number in the GEN_DATA result file (which has one number per line).
+Consider for example:
 
 .. code-block:: none