standard_expr_params 

Note: the following 3 attributes should always be used when using the exponential/exp_linear/sigmoidal form of expression.
These are only optional here, as whole attributeGroups can't be set as optional or required.

Attribute Group Information

Attributes

QName Type Fixed Default Use Inheritable Annotation
midpoint xs:string optional
rate xs:string optional
scale xs:string optional

Used By

Complex Types SteadyState, TimeCourse, Transition

Source 

<xs:attributeGroup name="standard_expr_params">
  <xs:annotation>
    <xs:documentation>Note: the following 3 attributes should always be used when using the exponential/exp_linear/sigmoidal form of expression. These are only optional here, as whole attributeGroups can't be set as optional or required.</xs:documentation>
  </xs:annotation>
  <xs:attribute name="rate" type="xs:string" use="optional"/>
  <xs:attribute name="scale" type="xs:string" use="optional"/>
  <xs:attribute name="midpoint" type="xs:string" use="optional"/>
</xs:attributeGroup>