Have \hskip revert back to a common command, when possible

lib/LaTeXML/Engine/TeX_Glue.pool.ltxml

@@ -26,20 +26,21 @@ use LaTeXML::Package;
 # \vskip            c  inserts vertical glue in a vertical list.
 # \unskip           c  removes a glue item from the current list.
 
-our @spaces = (    # Spaces to fake spacing, with width in ems
-  [0.100, "\x{200A}"],    # Hair space (thinner than thin space)
-  [0.167, "\x{2006}"],    # six-per-em
-  [0.200, "\x{2009}"],    # five-per-em, thin space
-  [0.250, "\x{2005}"],    # four-per-em, mid space
-  [0.333, "\x{2004}"],    # three-per-em, thick space
-  [0.500, "\x{2002}"],    # en-quad, "nut"
-  [1.000, "\x{2003}"],    # em-quad, "mutton"
+our @spaces = (    # Spaces to fake spacing, with width in ems, along with the common command
+  [0.100, "\x{200A}"],                                # Hair space (thinner than thin space)
+  [0.167, "\x{2006}"],                                # six-per-em
+  [0.200, "\x{2009}",         T_CS('\thinspace')],    # five-per-em, thin space
+  [0.250, "\x{2005}",         T_CS('\>')],            # four-per-em, mid space
+  [0.333, "\x{2004}",         T_CS('\;')],            # three-per-em, thick space
+  [0.500, "\x{2002}",         T_CS('\enspace')],      # en-quad, "nut"
+  [1.000, "\x{2003}",         T_CS('\quad')],         # em-quad, "mutton"
+  [2.000, "\x{2003}\x{2003}", T_CS('\qquad')],
 );
 
 # String of spacing chars with width roughly equivalent to $dimen
 sub DimensionToSpaces {
   my ($dimen) = @_;
-  my $fs      = LookupValue('font')->getSize;    # 1 em
+  my $fs      = LookupValue('font')->getSize;         # 1 em
   my $ems     = $dimen->ptValue / $fs;
   my $s       = '';
   for (my $i = $#spaces ; ($i >= 0) && ($ems > 0) ; $i--) {
@@ -49,6 +50,16 @@ sub DimensionToSpaces {
       $ems -= $n * $w; $s .= $spaces[$i][1] x $n; } }
   return $s; }
 
+# Revert a skip to it's (common) command, falling back to a generic \hskip <dim>
+sub revertSkip {
+  my ($command, $dimen) = @_;
+  my $fs  = LookupValue('font')->getSize;    # 1 em
+  my $ems = $dimen->ptValue / $fs;
+  for (my $i = 0 ; ($i <= $#spaces) ; $i++) {
+    next if ($ems > $spaces[$i][0] + 0.01) || !$spaces[$i][2];
+    return $spaces[$i][2] if $ems < $spaces[$i][0] + 0.01; }
+  return Invocation($command, $dimen); }
+
 # \hskip handled similarly to \kern
 # \hskip can be ignored in certain situations...
 DefConstructor('\hskip Glue', sub {
@@ -68,6 +79,7 @@ DefConstructor('\hskip Glue', sub {
     else {
       #      $document->openText(DimensionToSpaces($length), $props{font}); } },
       $document->absorb(DimensionToSpaces($length)); } },
+  reversion  => sub { revertSkip(T_CS('\hskip'), $_[1]); },
   properties => sub {
     my ($stomach, $length) = @_;
     (width => $length, isSpace => 1, isSkip => 1); });