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Section 3.1: Free Format Overview Up Section 3.1: Free Format Overview Subsection 3.1.2

### 3.1.1 Format Specification Versions

This document describes version 3.0 of the FEBio input specification. This format differs in several aspects from the previous versions of the input specification. This section describes the major changes between the different versions.
• Version 3.0: The latest and recommended version of the FEBio input specification described in this document. The major focus of this revision was adding support for FEBio 3.0's features for modeling heterogeneous parameters. Heterogeneous parameters can be created via mathematical expressions or via the MeshData section. It also introduces a more consistent way for referencing model parameters. The Geometry section was replaced with the Mesh and MeshDomains sections in order to further separate the definition of the mesh and its physical attributes (e.g. material assignments).
• Version 2.5: This format differs from its predecessor in some important aspects: all nodesets, surfaces, etc., that are used by boundary conditions, loads, contact, etc., must be defined in the Geometry section. Boundary conditions, loads, contact, etc., are now defined by referencing the sets in the Geometry section. This format also adds the MeshData section and reformats the Discrete section. Rigid node sets and prescribed rigid degrees of freedom are moved to the Boundary section. This format is still supported but considered obsolete.
• Version 2.0: This is the first major revision of the input file format and redefines many of the file sections: The Elements section uses a different organization. Elements are now grouped by material and element type. Multiple Elements sections can now be defined to create multiple parts. Surfaces can now be defined in the Geometry section and referenced by boundary conditions and contact definitions. A new Contact section contains all the contact definitions. A new Discrete section was defined that contains all the materials and definitions of the discrete elements (e.g. springs). The Boundary section is also redesigned. This format is still supported but considered obsolete.
• Version 1.3: This was an experimental version that redefined the Geometry section, but was later abandoned in favor of version 2.0. This version is no longer supported.
• Version 1.2: A Loads section was added and all surface and body loads are now defined in this section instead of the Boundary section. This version is mostly supported but considered obsolete.
• Version 1.1: Rigid body constraints are no longer defined in the rigid material definition but instead placed in a new Constraints section. This version is no longer supported.
• Version 1.0: The original input format specification. This version is no longer supported.
As of FEBio 3.0, only versions 1.2, 2.0, 2.5 are supported. Versions 1.2 and 2.0 are considered obsolete and it is highly recommended to convert older files to the new 3.0 specification for use with newer versions of FEBio. This can be done for instance using FEBioStudio.
Section 3.1: Free Format Overview Up Section 3.1: Free Format Overview Subsection 3.1.2