The OGS input file parameters are documented in the page hierarchy rooted here. A project file has the ending .prj and is a valid XML document. To check proper formatting you can use xmllint, see usage instructions in the documentation.

Depending on the type of the parameters the corresponding page titles have different prefixes, namely:

[tag] if the parameter is an XML tag in the input file
Example: [tag] linear_solvers
[attr] if the parameter is an attribute of an XML tag in the input file
Example: [attr] x
[case] either on the top level of the documentation tree, or to distinguish between different cases (i.e., sets of configuration options, which usually also means different underlying C++ types) in the input file.
Usually one can choose one of several cases by specifying the associated <type> tag in the input file.
Example: [tag] linear_solver and [case] Constant (<type>Constant</type>) vs. [case] MeshNode (<type>MeshNode</type>)

The input file parameters are documented within a tree structure (cf. the navigation tree on the left). This structure resembles the XML document tree of the input files, however, there are some small differences (see below).

Currently two different input files are documented: The project file (prj) and the geometry file (gml). All other cases on the top level do not represent separate input files but rather are shortcuts to certain project file sections, which are provided only in order to keep the documentation tree flat, they have no other special meaning.

A path in the documentation tree corresponds to a path in the prj or gml input file, e.g., [tag] boundary_condition corresponds to the path process_variables.process_variable.boundary_conditions.boundary_condition in the project file (here parent and child tags are separated by a dot).
Note: The top level XML tags (i.e., <OpenGeoSysProject> and <OpenGeoSysGLI>) have been omitted in the entire documentation for the sake of brevity.

There are two exceptions to this rule, both related to the [case] prefix:

Cases at the top level do not translate to XML tags. The cases [case] prj and [case] gml mark the root of the prj and gml input file, respectively. All other top level cases, however, belong somewhere in the project file XML tree. You can see where they belong in the Additional Info section of the [tag] and [attr] pages, e.g., [tag] geometry of the boundary condition has the full XML tag path process_variables.process_variable.boundary_conditions.boundary_condition.geometry.
Cases that distinguish types do not translate to XML tags either. They enclose a set of configuration settings that can be used at that specific point.
Example: There is a MeshNode initial condition, which has a field_name tag. I.e., if you configure the MeshNode parameter, you can (or must) specify the XML tag with the path parameters.parameter.field_name in the project file.
A MeshNode parameter can be defined by setting the parameters.parameter.type tag to MeshNode.

Further Information

Child parameters, attributes and cases

Used in the following test data files