A "common word" is a word that is so common (eg "the", "and", "he", "she") that it is ignored in searches UNLESS either preceded by a hash character (#) or a plus sign (+). For example, "#the common law #of Australia" will find that exact phrase. Without the #, the common words would be placeholders for any word, so you might also find the phrase "very common law from Australia".
This is the list of common words used by AustLII.
<% $common %><& ../footer &> <%init> my $common = ''; if ( open(FILE, " ) { my @words = split(/\s+/, $_); foreach my $w ( @words ) { next if ( $w eq '' ); if ( substr($w, 0, 1) ne $last_char ) { if ( $last_char ne '' ) { $common .= "\n"; } $last_char = substr($w, 0, 1); $common .= "
| $last_char:" . " | "; } $common .= $w . ' '; } } $common .= ' |