There seems to be a minor issue with the forward slash placement between weight and sizes. To resolve this, consider combining into one regex pattern where everything except anchors is optional. This will help align things properly to avoid 'normal' appearing on most variables.

Edit I came across a reference that details how CSS Font Shorthand Property parsing works: http://www.w3schools.com/cssref/pr_font_font.asp

edit2 The hard spaces delimiters have been adjusted to come after the optional parts and between the required parts.

 #  /(?:(?:(normal|italic|oblique|initial|inherit)\s+)?(?:(normal|small-caps|initial|inherit)\s+)?(?:((?:normal|bold|bolder|lighter|initial|inherit|\d+))\s+)?(?:(smaller|small|x-small|xx-small|medium|larger|large|x-large|xx-large|initial|inherit|\d+(?:\%|in|cm|mm|em|rem|ex|pt|pc|px))(?:\/(normal|initial|inherit|\d+(?:\%|in|cm|mm|em|rem|ex|pt|pc|px)))?\s+)(?:(initial|inherit|(?:"[^"]*"|'[^']*'|[a-zA-Z-]+)(?:\s*,\s*(?:"[^"]*"|'[^']*'|[a-zA-Z-]+))*))|(caption|icon|menu|message-box|small-caption|status-bar|initial|inherit))/

 ####  CSS - Font Shorthand Property  
 ####  Reference:  http://www.w3schools.com/cssref/pr_font_font.asp    
 #### --------------------------------
 #### font:     

 (?:
      #### User Defined Fonts
      #### ------------------

      ##### Style (optional)
      (?:
           (                        # (1 start), Style
                normal
             |  italic
             |  oblique
             |  initial
             |  inherit 
           )                        # (1 end)
           \s+   # delimiter
      )?

      ##### Variant (optional)
      (?:
           (                        # (2 start), Variant
                normal
             |  small-caps
             |  initial
             |  inherit 
           )                        # (2 end)
           \s+   # delimiter
      )?

      ##### Weight (optional)
      (?:
           (                        # (3 start), Weight
                (?:
                     normal
                  |  bold
                  |  bolder
                  |  lighter
                  |  initial
                  |  inherit 
                  |  \d+ 
                )
           )                        # (3 end)
           \s+   # delimiter
      )?

      ##### Size (required)
      (?:
           (                        # (4 start), Size
                smaller
             |  small
             |  x-small
             |  xx-small
             |  medium
             |  larger
             |  large
             |  x-large
             |  xx-large
             |  initial
             |  inherit
             |  \d+ 
                (?: \% | in | cm | mm | em | rem | ex | pt | pc | px )
           )                        # (4 end)

           #####  Line Height (optional)
           (?:
                /                   # Separator
                (                   # (5 start), Line height
                     normal
                  |  initial
                  |  inherit
                  |  \d+ 
                     (?: \% | in | cm | mm | em | rem | ex | pt | pc | px )
                )                   # (5 end)

           )?

           \s+   # delimiter 
      )

      ##### Family (required)
      (?:
           (                        # (6 start), Family
                initial
             |  inherit
             |  (?: " [^"]* " | ' [^']* ' | [a-zA-Z-]+ )
                (?:
                     \s* , \s* 
                     (?: " [^"]* " | ' [^']* ' | [a-zA-Z-]+ )
                )*
           )                        # (6 end)
      )

   |  

      #### OR, 
      #### Use the Fonts used by these OS elements
      #### ------------------

      #### Values (required, if used)
      (                             # (7 start), Use values
           caption
        |  icon
        |  menu
        |  message-box
        |  small-caption
        |  status-bar
        |  initial
        |  inherit
      )                             # (7 end)
 )

Perl Test case

$str = 'font:normal small-caps 120%/120% "Times New Roman", sans-serif;';

if ( $str =~ /(?:(?:(normal|italic|oblique|initial|inherit)\s+)?(?:(normal|small-caps|initial|inherit)\s+)?(?:((?:normal|bold|bolder|lighter|initial|inherit|\d+))\s+)?(?:(smaller|small|x-small|xx-small|medium|larger|large|x-large|xx-large|initial|inherit|\d+(?:\%|in|cm|mm|em|rem|ex|pt|pc|px))(?:\/(normal|initial|inherit|\d+(?:\%|in|cm|mm|em|rem|ex|pt|pc|px)))?\s+)(?:(initial|inherit|(?:"[^"]*"|'[^']*'|[a-zA-Z-]+)(?:\s*,\s*(?:"[^"]*"|'[^']*'|[a-zA-Z-]+))*))|(caption|icon|menu|message-box|small-caption|status-bar|initial|inherit))/)
{
    print "\nmatched  '$&'\n\n";
    print "style   = '$1'\n";
    print "variant = '$2'\n";
    print "weight  = '$3'\n";
    print "size    = '$4'\n";
    print "height  = '$5'\n";
    print "family  = '$6'\n";
    print "values  = '$7'\n";
}

Output >>

matched  'normal small-caps 120%/120% "Times New Roman", sans-serif'

style   = 'normal'
variant = 'small-caps'
weight  = ''
size    = '120%'
height  = '120%'
family  = '"Times New Roman", sans-serif'
values  = ''

Here is a method you can use to manipulate attributes in a string:

Start by identifying one attribute and then removing it from the original string. Proceed to search for the next attribute in the updated string.

Below is an illustration focusing on the primary attribute within the string:

var str = decl.val;

function removeFromString(str, result) {
    console.log(result);
    return str.slice(0, result.index) + str.slice(result.index + result[0].length);
}

var style = str.match(/\s*(?:\s*(normal|italic|oblique)){1}/i); 
if(style) {
    str = removeFromString(str, style);
}
style = style ? style[1] : "";

To visualize this process, I have created a JSFiddle.