v3 canvas: relax requirement for extent info

lib/iiif/v3/presentation/canvas.rb

@@ -51,14 +51,18 @@ def validate
           # It may have width, height and duration.""
           height = self['height']
           width = self['width']
-          extent_err_msg = "#{self.class} must have (a height and a width) and/or a duration"
           if (!!height ^ !!width) # this is an exclusive or: forces height and width to boolean
+            extent_err_msg = "#{self.class} requires both height and width or neither"
             raise IIIF::V3::Presentation::IllegalValueError, extent_err_msg
           end
-          duration = self['duration']
-          unless (height && width) || duration
-            raise IIIF::V3::Presentation::IllegalValueError, extent_err_msg
-          end
+          # NOTE:  relaxing requirement for (exactly one width and one height, and/or exactly one duration)
+          #  as Stanford has objects (such as txt files) for which this makes no sense
+          #  (see sul-dlss/purl/issues/169)
+          # duration = self['duration']
+          # unless (height && width) || duration
+          #   extent_err_msg = "#{self.class} must have (a height and a width) and/or a duration"
+          #   raise IIIF::V3::Presentation::IllegalValueError, extent_err_msg
+          # end
 
           # TODO: Content must not be associated with space or time outside of the Canvas’s dimensions,
           # such as at coordinates below 0,0, greater than the height or width, before 0 seconds, or after the duration.

spec/unit/iiif/v3/presentation/canvas_spec.rb

@@ -75,7 +75,9 @@ def initialize(hsh={})
       expect { subject.validate }.to raise_error(IIIF::V3::Presentation::IllegalValueError, exp_id_err_msg)
     end
 
-    let(:exp_extent_err_msg) { "#{described_class} must have (a height and a width) and/or a duration" }
+    # let(:exp_extent_err_msg) { "#{described_class} must have (a height and a width) and/or a duration" }
+    #  (see sul-dlss/purl/issues/169)
+    let(:exp_extent_err_msg) { "#{described_class} requires both height and width or neither" }
     it 'raises an IllegalValueError if height is a string' do
       subject['height'] = 'foo'
       expect { subject.validate }.to raise_error(IIIF::V3::Presentation::IllegalValueError, exp_extent_err_msg)
@@ -90,6 +92,8 @@ def initialize(hsh={})
       expect { subject.validate }.to raise_error(IIIF::V3::Presentation::IllegalValueError, exp_extent_err_msg)
     end
     it 'raises an IllegalValueError if no width, height or duration' do
+      # (see sul-dlss/purl/issues/169)
+      skip('while this is in the current v3 spec, it does not make sense for some content (e.g. txt files)')
       expect { subject.validate }.to raise_error(IIIF::V3::Presentation::IllegalValueError, exp_extent_err_msg)
     end
     it 'allows width, height and duration' do