DOC: update docstrings for ignore_blank, writeto()

astropy/io/fits/hdu/base.py

@@ -374,7 +374,7 @@ def readfrom(cls, fileobj, checksum=False, ignore_missing_end=False, **kwargs):
     def writeto(self, name, output_verify="exception", overwrite=False, checksum=False):
         """
         Write the HDU to a new file. This is a convenience method to
-        provide a user easier output interface if only one HDU needs
+        provide a user friendly output interface if only one HDU needs
         to be written to a file.
 
         Parameters
@@ -1600,9 +1600,9 @@ def match_header(cls, header):
 
     def writeto(self, name, output_verify="exception", overwrite=False, checksum=False):
         """
-        Works similarly to the normal writeto(), but prepends a default
-        `PrimaryHDU` are required by extension HDUs (which cannot stand on
-        their own).
+        Works similarly to :func:`_BaseHDU.writeto`, but prepends a default
+        `PrimaryHDU` as required by extension HDUs (which cannot be written
+        on their own).
         """
         from .hdulist import HDUList
         from .image import PrimaryHDU

astropy/io/fits/hdu/image.py

@@ -779,9 +779,9 @@ def _convert_pseudo_integer(self, data):
         Handle "pseudo-unsigned" integers, if the user requested it.  Returns
         the converted data array if so; otherwise returns None.
 
-        In this case case, we don't need to handle BLANK to convert it to NAN,
-        since we can't do NaNs with integers, anyway, i.e. the user is
-        responsible for managing blanks.
+        Handling of BLANK is done outside of this function on the converted
+        uint data, meaning that BLANK needs to be shifted by BZERO as well
+        before conversion of the corresponding values to NaN.
         """
         dtype = self._dtype_for_bitpix()
         # bool(dtype) is always False--have to explicitly compare to None; this