relax a requirement

relax requirement that all labels for all interactions must be defined

doc/src/read_data.rst

@@ -623,10 +623,10 @@ integers (1, not 1.0).
 
 Type labels can be used to make data files more general, by defining
 atom, bond, etc. types in terms of user-provided strings instead of
-numbers.  If a type label section exists for any one interaction
+numbers.  If a type label section exists for a given interaction
 (atom, bond, angle, dihedral or improper), then all types must be
-assigned a type label for all interactions.  All type label sections
-must come before any section that includes types.  The numeric types
+assigned a type label for that interaction.  Type label sections must
+come before any section that utilizes that type.  The numeric types
 listed in the *Atoms*, *Bonds*, etc. section are first converted into
 their corresponding type label before being read into LAMMPS; type
 labels cannot be directly substituted for numeric types used in data

doc/src/write_data.rst

@@ -109,8 +109,10 @@ from :doc:`fix property/atom <fix_property_atom>`.
 The *nolabelmap* keyword requests that the default label map should
 not be written to the data file (see the Type Label sections of
 :doc:`read_data <read_data>` command for details). By default, if the
-default label map is fully defined, i.e. every atom, bond, etc. type
-has an associated type label, it is written to the data file.
+default label map is fully defined for a given interaction, i.e. every
+atom, bond, angle, dihedral or improper type has an associated type
+label, then a type label section for that interaction is written to
+the data file.
 
 The *pair* keyword lets you specify in what format the pair
 coefficient information is written into the data file.  If the value