bounds attributes clarity

appa.adoc

@@ -8,7 +8,8 @@ All CF attributes are listed here except for those that are used to describe gri
 See Appendix F for the grid mapping attributes, and Appendix K for mesh topology attributes.
 
 The "Type" values are **S** for string, **N** for numeric, and **D** for the type of the data variable.
-The "Use" values are **G** for global, **Gr** for applying to groups, **C** for variables containing coordinate data, **D** for data variables, **M** for geometry container variables, **Do** for domain variables, **BI** for  for attributes inherited by boundary variables, **BO** for attributes owned by boundary variables, and **-** for variables with a special purpose.
+Each attribute may be used in any of the ways shown in its "Use" entry.
+**G** indicates it can appear as a global attribute, and **Gr** as a group attribute; if use of an attribute is restricted to certain kinds of variables this is indicated as follows: **C** for variables containing coordinate data, **D** for data variables, **M** for geometry container variables, **Do** for domain variables, **BI** and **BO** for boundary variables (see <<cell-boundaries>> for the distinction between **BI** and **BO**), and **-** for variables with some other purpose.
 "Links" indicates the location of the attribute"s original definition (first link) and sections where the attribute is discussed in this document (additional links as necessary).
 
 [[table-attributes]]

ch07.adoc

@@ -23,8 +23,8 @@ __A boundary variable will have one more dimension than its associated coordinat
 
 A boundary variable inherits the values of some attributes from its parent coordinate variable.
 If a coordinate variable has any of the attributes marked "BI" (for "inherit") in the "Use" column of <<attribute-appendix>>, they are assumed to apply to its bounds variable as well.
-It is recommended not to include any of these attributes on a bounds variable, but it is technically not forbidden to include a BI attribute as long as it is also present in the parent coordinate variable.
-If such an attribute is included then it must match exactly the parent variable's attribute, i.e. the data type and value must be exactly the same.
+It is recommended that BI attributes not be included on a boundary variable.
+If a BI attribute is included, it must also be present in the parent variable, and it must exactly match the parent attribute's data type and value.
 A boundary variable can only have inheritable attributes if they are also present on its parent coordinate variable.
 A bounds variable may have any of the attributes marked "BO" for ("own") in the "Use" column of <<attribute-appendix>>.
 These attributes take precedence over any corresponding attributes of the parent variable.