Spec: clarify that bounds of variant field must not have bounds for mixed types

format/spec.md

@@ -666,7 +666,7 @@ Notes:
 
 For Variant, values in the `lower_bounds` and `upper_bounds` maps store serialized Variant objects that contain lower or upper bounds respectively. The object keys for the bound-variants are normalized JSON path expressions that uniquely identify a field. The object values are primitive Variant representations of the lower or upper bound for that field. Including bounds for any field is optional and upper and lower bounds must have the same Variant type.
 
-Bounds for a field must be accurate for all non-null values of the field in a data file. Bounds for values within arrays must be accurate all values in the array. Bounds must not be written to describe values with mixed Variant types (other than null). For example, a "measurement" field that contains int64 and null values may have bounds, but if the field also contained a string value such as "n/a" or "0" then the field may not have bounds.
+Bounds for a field must be accurate for all non-null values of the field in a data file. Bounds for values within arrays must be accurate all values in the array. Bounds must not be written to describe values with mixed Variant types (other than null). For example, a "measurement" field that contains int64 and null values may have bounds, but if the field also contained a string value such as "n/a" or "0" then the field must not have bounds.
 
 The Variant bounds objects are serialized by concatenating the [Variant encoding](https://github.com/apache/parquet-format/blob/master/VariantEncoding.md) of the metadata (containing the normalized field paths) and the bounds object.
 Field paths follow the JSON path format to use normalized path, such as `$['location']['latitude']` or `$['user.name']`. The special path `$` represents bounds for the variant root, indicating that the variant data consists of uniform primitive types, such as strings.