- Which feature equations should be required to be present in
**inp**in order for the match to succeed. - Which feature equations should be generated in the output tree as a function of the feature equations in the input tree.

*Require & Retain:*The feature equation is required to be in**inp**in order for matching to succeed. Upon matching, the equation will be copied to the output tree. To achieve this behaviour, the equation must be placed in the**lhs**tree of the metarule preceded by a plus character (e.g. +*V*.*t*:<*trans*>=+).^{27.9}*Require & Don't Copy:*The equation is required to be in**inp**for matching, but should not be copied to the output tree. To have this behavior, the equation must be in**lhs**preceded by the minus character (e.g. -*NP*_{1}:<*case*>=*acc*).-
*Negative Requirement:*In order for matching to succeed the equation should not be found in**inp**. This is achieved by including the equation in**lhs**preceded by a caret (e.g., <*tex*2*html*_{v}*erb*_{m}*ark*>1<*tex*2*html*_{v}*erb*_{m}*ark*>*V*.*b*:<*passive*>=-). *Optional & Don't Copy:*The equation is not required for matching, but we have to make sure not to copy it to the output tree set of equations, regardless of it being present or not in**inp**. Those equations must be in**lhs**in raw form, i.e., neither preceded by a plus nor minus character (e.g.*S*_{r}.*b*:<*perfect*>=*VP*.*t*:<*perfect*>).*Optional & Retain:*The equation is not required for matching, but in case it is found in**inp**it must be copied to the output tree. This is the*default*case, and hence these equations should not be present in the metarule specification.*Add:*The equation is not required for matching but we want it to be put in the output tree anyway. These equations are placed in raw form in the**rhs**(notice in this case it is the right hand side tree).

D*name1*
*dummy1*
*name2*

where ``D'' is a single character that specifies the directive,
as listed below;
- replace
*name1*with*name2*in all equations from the input tree. - |:
- exchange
*name1*and*name2*in all equations from the input tree. - !:
- remove all equations where
*name1*appears (here,*name2*is also dummy).

- The (typed) variables in the equations at
**lhs**and**rhs**are substituted by the names of the nodes they have been instantiated to. - The requirements concerning feature equations are checked, according to the above rules.
- If the match survives feature equation checking, the proper output tree is generated, according to Section C.2.3 and to the rules described above for the feature equations.