DOC: Small changes to PaperSize notes (#2834)

Plus one typo in xmp.py.

pypdf/papersizes.py

@@ -11,16 +11,17 @@ class Dimensions(NamedTuple):
 class PaperSize:
  """(width, height) of the paper in portrait mode in pixels at 72 ppi."""
 
- # Notes how to calculate it:
- # 1. Get the size of the paper in mm
- # 2. Convert it to inches (25.4 millimeters are equal to 1 inches)
- # 3. Convert it to pixels ad 72dpi (1 inch is equal to 72 pixels)
+ # Notes of how to calculate it:
+ # 1. Get the size of the paper in millimeters
+ # 2. Convert it to inches (25.4 millimeters is equal to 1 inch)
+ # 3. Convert it to pixels at 72dpi (1 inch is equal to 72 pixels)
 
  # All Din-A paper sizes follow this pattern:
- # 2xA(n-1) = A(n)
+ # 2 x A(n - 1) = A(n)
  # So the height of the next bigger one is the width of the smaller one
- # The ratio is always approximately the ratio 1:2**0.5
+ # The ratio is always approximately 1:2**0.5
  # Additionally, A0 is defined to have an area of 1 m**2
+ # https://en.wikipedia.org/wiki/ISO_216
  # Be aware of rounding issues!
  A0 = Dimensions(2384, 3370) # 841mm x 1189mm
  A1 = Dimensions(1684, 2384)

pypdf/xmp.py

@@ -306,7 +306,7 @@ def _get_text(self, element: XmlElement) -> str:
  """Unique identifier of the work from which this resource was derived."""
 
  dc_subject = property(_getter_bag(DC_NAMESPACE, "subject"))
- """An unordered array of descriptive phrases or keywrods that specify the
+ """An unordered array of descriptive phrases or keywords that specify the
  topic of the content of the resource."""
 
  dc_title = property(_getter_langalt(DC_NAMESPACE, "title"))