ispell-skip-html

ispell-skip-html is a variable defined in `ispell.el'.
Its value is

use-mode-name

• Automatically becomes buffer-local when set.

Documentation:
Indicates whether ispell should skip spell checking of SGML markup.
If t, always skip SGML markup; if nil, never skip; if non-t and non-nil,
guess whether SGML markup should be skipped according to the name of the
buffer's major mode.

You can customize this variable.