Sure. To get an annotated description:

use YAPE::Regex::Explain;
my $pattern='(\n\s*[0-9]{1,3}\s*\n\s*<page>\s*\n|\n\s*-[0-9]{1,3}-\s*\
+n\s*<page>\s*\n|\n\s*[A-Za-z]-[0-9]{1,3}\s*\n\s*<page>\s*\n|\n\s*page
+\s*[0-9]{1,3}\s*of\s*[0-9]{1,3}\s*\n)';

print YAPE::Regex::Explain->new($pattern)->explain;
[download]

which produces:

The regular expression:

(?-imsx:(\n\s*[0-9]{1,3}\s*\n\s*<page>\s*\n|\n\s*-[0-9]{1,3}-\s*\n\s*<
+page>\s*\n|\n\s*[A-Za-z]-[0-9]{1,3}\s*\n\s*<page>\s*\n|\n\s*page\s*[0
+-9]{1,3}\s*of\s*[0-9]{1,3}\s*\n))

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    [0-9]{1,3}               any character of: '0' to '9' (between 1
                             and 3 times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    <page>                   '<page>'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    -                        '-'
----------------------------------------------------------------------
    [0-9]{1,3}               any character of: '0' to '9' (between 1
                             and 3 times (matching the most amount
                             possible))
----------------------------------------------------------------------
    -                        '-'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    <page>                   '<page>'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    [A-Za-z]                 any character of: 'A' to 'Z', 'a' to 'z'
----------------------------------------------------------------------
    -                        '-'
----------------------------------------------------------------------
    [0-9]{1,3}               any character of: '0' to '9' (between 1
                             and 3 times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    <page>                   '<page>'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    page                     'page'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    [0-9]{1,3}               any character of: '0' to '9' (between 1
                             and 3 times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    of                       'of'
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    [0-9]{1,3}               any character of: '0' to '9' (between 1
                             and 3 times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \n                       '\n' (newline)
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]

Now, if you would tell us something about the context in which this is used (other than just that it is used on html), maybe a higher-level description would be possible.