diff --git a/doc/manual/source/the-model-file.rst b/doc/manual/source/the-model-file.rst
index b7f37d5fb740eacee0b4235120c50a6127356dcf..d939b107a0ff6c63a8af7cff50c3f7a2f5196b4d 100644
--- a/doc/manual/source/the-model-file.rst
+++ b/doc/manual/source/the-model-file.rst
@@ -4933,7 +4933,10 @@ All of these elements are discussed in the following.
 
     .. option:: filter_use_relaxation
 
-       ..
+       Triggers relaxation within the guess and verify algorithm used in the update step of the piecewise
+       Kalman filter. When old and new guess regime differ to much, use a new guess closer to the previous guess.
+       In case of multiple solutions, tends to provide an occasionally binding regime with a shorter duration (typically preferable).
+       Specifying this option may slow down convergence. Default: not enabled.
 
    *Output*