diff --git a/lib/CSS/Specification/Build.rakumod b/lib/CSS/Specification/Build.rakumod
index 3dbd493..dac8eb4 100755
--- a/lib/CSS/Specification/Build.rakumod
+++ b/lib/CSS/Specification/Build.rakumod
@@ -1,214 +1,249 @@
-unit module CSS::Specification::Build;
+#!/usr/bin/env raku
 
-use CSS::Specification;
-use CSS::Specification::Actions;
-use CSS::Specification::Compiler;
-my subset Path where Str|IO::Path;
-use experimental :rakuast;
+#= translates w3c property definitions to basic Raku roles, grammars or actions.
 
-#= generate parsing grammar
-our proto sub generate(|) { * };
-multi sub generate('grammar', Str $grammar-name, Path :$input-path?) {
+module CSS::Specification::Build {
 
-    my CSS::Specification::Actions $actions .= new;
-    my CSS::Specification::Compiler $compiler .= new: :$actions;
-    my @defs = $compiler.load-defs($input-path);
+    use CSS::Specification;
+    use CSS::Specification::Actions;
+    my subset Path where { ($_//Str) ~~ Str|IO::Path };
 
-    say qq:to<END-HDR>;
-    use v6;
-    #  -- DO NOT EDIT --
-    # generated by: {($*PROGRAM-NAME, @*ARGS.Slip).join: ' '};
+    #= generate parsing grammar
+    our proto sub generate(Str $type, Str $name, Path :$input-path?) { * };
+    multi sub generate('grammar', Str $grammar-name, Path :$input-path?) {
 
-    unit grammar {$grammar-name};
-    END-HDR
+        my CSS::Specification::Actions $actions .= new;
+        my @defs = load-defs($input-path, $actions);
 
-    generate-raku-rules(@defs);
-}
+        say qq:to<END-HDR>;
+        use v6;
+        #  -- DO NOT EDIT --
+        # generated by: {($*PROGRAM-NAME, @*ARGS.Slip).join: ' '};
 
-#= generate actions class
-multi sub generate('actions', Str $class-name, Path :$input-path?) {
+        unit grammar {$grammar-name};
+        END-HDR
 
-    my CSS::Specification::Actions $actions .= new;
-    my CSS::Specification::Compiler $compiler .= new: :$actions;
-    my @defs = $compiler.load-defs($input-path);
+        generate-raku-rules(@defs);
+    }
 
-    say qq:to<END-HDR>;
-    use v6;
-    #  -- DO NOT EDIT --
-    # generated by: {($*PROGRAM-NAME, @*ARGS.Slip).join: ' '}
+    #= generate actions class
+    multi sub generate('actions', Str $class-name, Path :$input-path?) {
 
-    unit class {$class-name};
-    END-HDR
+        my CSS::Specification::Actions $actions .= new;
+        my @defs = load-defs($input-path, $actions);
 
-    my %prop-refs = $actions.prop-refs;
-    generate-raku-actions(@defs, %prop-refs);
-}
+        say qq:to<END-HDR>;
+        use v6;
+        #  -- DO NOT EDIT --
+        # generated by: {($*PROGRAM-NAME, @*ARGS.Slip).join: ' '}
 
-multi sub generate('interface', $role-name, :$input-path? --> RakuAST::Package:D) is DEPRECATED {
+        unit class {$class-name};
+        END-HDR
 
-    my CSS::Specification::Actions $actions .= new;
-    my CSS::Specification::Compiler $compiler .= new: :$actions;
-    my @role-id = $role-name.split('::');
-    $compiler.load-defs($input-path);
-    $compiler.role-ast(@role-id);
-}
+        my %prop-refs = $actions.prop-refs;
+        generate-raku-actions(@defs, %prop-refs);
+    }
 
-#= generate interface roles.
-multi sub generate('interface', @role-id, Path :$input-path? --> RakuAST::Package:D) {
+    #= generate interface roles.
+    multi sub generate('interface', Str $role-name, Path :$input-path?) {
 
-    my CSS::Specification::Actions $actions .= new;
-    my CSS::Specification::Compiler $compiler .= new: :$actions;
-    $compiler.load-defs($input-path);
-    $compiler.role-ast(@role-id);
-}
+        my CSS::Specification::Actions $actions .= new;
+        my @defs = load-defs($input-path, $actions);
 
-sub find-edges(%properties, %child-props) {
-    # match boxed properties with children
-    for %properties.pairs {
-        my $key = .key;
-        my $value = .value;
-        unless  $key ~~ / top|right|bottom|left / {
-            # see if the property has any children
-            for <top right bottom left> -> $side {
-                # find child. could be xxxx-side (e.g. margin-left)
-                # or xxx-yyy-side (e.g. border-left-width);
-                for $key ~ '-' ~ $side, $key.subst("-", [~] '-', $side, '-') -> $edge {
-                    if $edge ne $key
-                    && (%properties{$edge}:exists) {
-                        my $prop = %properties{$edge};
-                        $prop<edge> = $key;
-                        $value<edges>.push: $edge;
-                        $value<box> ||= True;
-                        last;
+        say qq:to<END-HDR>;
+        use v6;
+        #  -- DO NOT EDIT --
+        # generated by: {($*PROGRAM-NAME, @*ARGS.Slip).join: ' '}
+        unit role {$role-name};
+        END-HDR
+
+        my %prop-refs = $actions.prop-refs;
+        my %props = $actions.props;
+        my %rules = $actions.rules;
+        generate-raku-interface(%prop-refs, %props, %rules);
+    }
+
+    sub find-edges(%properties, %child-props) {
+        # match boxed properties with children
+        for %properties.pairs {
+            my $key = .key;
+            my $value = .value;
+            unless  $key ~~ / top|right|bottom|left / {
+                # see if the property has any children
+                for <top right bottom left> -> $side {
+                    # find child. could be xxxx-side (e.g. margin-left)
+                    # or xxx-yyy-side (e.g. border-left-width);
+                    for $key ~ '-' ~ $side, $key.subst("-", [~] '-', $side, '-') -> $edge {
+                        if $edge ne $key
+                        && (%properties{$edge}:exists) {
+                            my $prop = %properties{$edge};
+                            $prop<edge> = $key;
+                            $value<edges>.push: $edge;
+                            $value<box> ||= True;
+                            last;
+                        }
                     }
                 }
             }
-        }
-        with %child-props{$key} {
-            for .unique -> $child-prop {
-                next if $value<edges> && $value<edges>{$child-prop};
-                my $prop = %properties{$child-prop};
-                # property may have multiple parents
-                $value<children>.push: $child-prop;
+            with %child-props{$key} {
+                for .unique -> $child-prop {
+                    next if $value<edges> && $value<edges>{$child-prop};
+                    my $prop = %properties{$child-prop};
+                    # property may have multiple parents
+                    $value<children>.push: $child-prop;
+                }
             }
+            # we can get defaults from the children
+            $value<default>:delete
+                if ($value<edges>:exists)
+                || ($value<children>:exists);
         }
-        # we can get defaults from the children
-        $value<default>:delete
-            if ($value<edges>:exists)
-            || ($value<children>:exists);
     }
-}
 
-sub check-edges(%properties) {
-    for %properties.pairs {
-        my $key = .key;
-        my $value = .value;
-        my $edges = $value<edges>;
+    sub check-edges(%properties) {
+        for %properties.pairs {
+            my $key = .key;
+            my $value = .value;
+            my $edges = $value<edges>;
 
-        note "box property doesn't have four edges $key: $edges"
-            if $edges && +$edges != 4;
+            note "box property doesn't have four edges $key: $edges"
+                if $edges && +$edges != 4;
 
-        my $children = $value<children>;
-        if $value<edge> && $children {
-            my $non-edges = $children.grep: { ! %properties{$_}<edge> };
-            note "edge property $key has non-edge properties: $non-edges"
-                if $non-edges;
+            my $children = $value<children>;
+            if $value<edge> && $children {
+                my $non-edges = $children.grep: { ! %properties{$_}<edge> };
+                note "edge property $key has non-edge properties: $non-edges"
+                    if $non-edges;
+            }
         }
     }
-}
-
-our sub summary(Path :$input-path? ) {
-
-    my CSS::Specification::Actions $actions .= new;
-    my CSS::Specification::Compiler $compiler .= new: :$actions;
-    my @defs = $compiler.load-defs($input-path);
-    my @summary;
-    my %properties;
-
-    for @defs -> $def {
 
-        with $def<props> -> @props {
-            my $raku = $def<raku>;
-            my $synopsis = $def<synopsis>;
-            my $box = $raku ~~ /:s '**' '1..4' $/;
-
-            for @props -> $name {
-                my %details = :$name, :$synopsis;
-                %details<default> = $_
-                    with $def<default>;
-                %details<inherit> = $_
-                    with $def<inherit>;
-                %details<box> = True
-                    if $box;
-                %properties{$name} = %details;
-                @summary.push: %details;
+    our sub summary(Path :$input-path? ) {
+
+        my CSS::Specification::Actions $actions .= new;
+        my @defs = load-defs($input-path, $actions);
+        my @summary;
+        my %properties;
+
+        for @defs -> $def {
+
+            with $def<props> -> @props {
+                my $raku = $def<raku>;
+                my $synopsis = $def<synopsis>;
+                my $box = $raku ~~ /:s '**' '1..4' $/;
+
+                for @props -> $name {
+                    my %details = :$name, :$synopsis;
+                    %details<default> = $_
+                        with $def<default>;
+                    %details<inherit> = $_
+                        with $def<inherit>;
+                    %details<box> = True
+                        if $box;
+                    %properties{$name} = %details;
+                    @summary.push: %details;
+                }
             }
         }
+
+        find-edges(%properties, $actions.child-props);
+        check-edges(%properties);
+
+        return @summary;
     }
 
-    find-edges(%properties, $actions.child-props);
-    check-edges(%properties);
+    sub load-defs (Path $properties-spec, $actions?) {
+        my $fh = $properties-spec
+            ?? open $properties-spec, :r
+            !! $*IN;
 
-    return @summary;
-}
+        my @defs;
 
+        for $fh.lines -> $prop-spec {
+            # handle full line comments
+            next if $prop-spec ~~ /^'#'/ || $prop-spec eq '';
+            # '| inherit' and '| initial' are implied anyway; get rid of them
+            my $spec = $prop-spec.subst(/\s* '|' \s* [inherit|initial]/, ''):g;
 
-sub generate-raku-rules(@defs) {
+            my $/ = CSS::Specification.subparse($spec, :actions($actions) );
+            die "unable to parse: $spec"
+                unless $/;
+            my $defs = $/.ast;
+            @defs.append: @$defs;
+        }
 
-    for @defs -> $def {
+        return @defs;
+    }
 
-        with $def<props> -> @props {
-            my $raku = $def<raku>;
-            my $synopsis = $def<synopsis>;
+    sub generate-raku-rules(@defs) {
 
-            # boxed repeating property. repeat the expr
-            my $box = $raku ~~ /:s '**' '1..4' $/
-                ?? ', :box'
-                !! '';
-            my $repeats = '';
-            if $box {
-                $raku ~~ s/:s '**' '1..4' $//;
-                $repeats = ' ** 1..4';
-            }
+        for @defs -> $def {
+
+            with $def<props> -> @props {
+                my $raku = $def<raku>;
+                my $synopsis = $def<synopsis>;
 
-            for @props -> $prop {
-                my $match = $prop.subst(/\-/, '\-'):g;
+                # boxed repeating property. repeat the expr
+                my $box = $raku ~~ /:s '**' '1..4' $/
+                    ?? ', :box'
+                    !! '';
+                my $repeats = '';
+                if $box {
+                    $raku ~~ s/:s '**' '1..4' $//;
+                    $repeats = ' ** 1..4';
+                }
 
+                for @props -> $prop {
+                    my $match = $prop.subst(/\-/, '\-'):g;
+
+                    say "";
+                    say "#| $prop: $synopsis";
+                    say "rule decl:sym<{$prop}> \{:i ($match) ':' <val( rx\{ <expr=.expr-{$prop}>$repeats \}, &?ROUTINE.WHY)> \}";
+                    say "rule expr-$prop \{:i $raku \}";
+                }
+            }
+            else {
+                my $rule = $def<rule>;
+                my $raku = $def<raku>;
+                my $synopsis = $def<synopsis>;
                 say "";
-                say "#| $prop: $synopsis";
-                say "rule decl:sym<{$prop}> \{:i ($match) ':' <val( rx\{ <expr=.expr-{$prop}>$repeats \}, &?ROUTINE.WHY)> \}";
-                say "rule expr-$prop \{:i $raku \}";
+                say "#| $rule: $synopsis";
+                say "rule $rule \{:i $raku \}";
             }
         }
-        else {
-            my $rule = $def<rule>;
-            my $raku = $def<raku>;
-            my $synopsis = $def<synopsis>;
-            say "";
-            say "#| $rule: $synopsis";
-            say "rule $rule \{:i $raku \}";
-        }
     }
-}
 
-sub generate-raku-actions(@defs, %references) {
+    sub generate-raku-actions(@defs, %references) {
 
-    for @defs -> $def {
+        for @defs -> $def {
 
-        my $synopsis = $def<synopsis>;
+            my $synopsis = $def<synopsis>;
 
-        with $def<props> -> @props {
-            for @props -> $prop {
+            with $def<props> -> @props {
+                for @props -> $prop {
 
-                say "method expr-{$prop}(\$/) \{ make \$.build.list(\$/) \}"
-                    if %references{'expr-' ~ $prop}:exists;
+                    say "method expr-{$prop}(\$/) \{ make \$.build.list(\$/) \}"
+                        if %references{'expr-' ~ $prop}:exists;
+                }
+            }
+            else {
+                my $rule = $def<rule>;
+                say "method $rule\(\$/\) \{ make \$.build.rule(\$/) \}"
             }
-        }
-        else {
-            my $rule = $def<rule>;
-            say "method $rule\(\$/\) \{ make \$.build.rule(\$/) \}"
         }
     }
-}
 
+    #= generate an interface class for all unresolved terms.
+    sub generate-raku-interface(%references, %prop-names, %rule-names) {
+
+        my %unresolved = %references;
+        %unresolved{'expr-' ~ $_}:delete
+            for %prop-names.keys;
+        %unresolved{$_}:delete
+            for %rule-names.keys;
 
+        for %unresolved.keys.sort -> $sym {
+            say "method {$sym}(\$/) \{ ... \}";
+        }
+    }
+}
diff --git a/lib/CSS/Specification/Compiler.rakumod b/lib/CSS/Specification/Compiler.rakumod
index 0808600..7dc0760 100644
--- a/lib/CSS/Specification/Compiler.rakumod
+++ b/lib/CSS/Specification/Compiler.rakumod
@@ -73,11 +73,10 @@ method !interface-methods {
 our proto sub compile (|) {*}
 
 multi sub compile(:@occurs! ($quant! is copy, *%term)) {
-    my RakuAST::Regex $separator;
-    my $atom = compile(|%term);
-    if $quant[0] ~~ '#' {
-        $separator = compile(:op<,>);
-    }
+    my RakuAST::Regex $atom = compile(|%term);
+    my RakuAST::Regex $separator = compile(:op<,>)
+        if $quant[0] ~~ '#';
+
     my RakuAST::Regex::Quantifier $quantifier = do given $quant {
         when '?' {
             RakuAST::Regex::Quantifier::ZeroOrOne.new
@@ -100,23 +99,34 @@ multi sub compile(:@occurs! ($quant! is copy, *%term)) {
 
 sub id(Str:D $id) {  RakuAST::Name.from-identifier($id) }
 
-sub assertion(Str:D $id, Bool :$capturing = True) {
-    my $name := $id.&id;
-    RakuAST::Regex::Assertion::Named.new(
-        :$name, :$capturing
+sub look-ahead(RakuAST::Regex::Assertion $assertion, Bool :$negated = False, Bool :$capturing = False) {
+    RakuAST::Regex::Assertion::Lookahead.new(
+        :$assertion, :$negated
     );
 }
 
-sub assertion-arg(Str:D $id, Str:D $arg, Bool :$capturing = True) {
+multi sub assertion(Str:D $id, Bool :$capturing = True, RakuAST::ArgList :$args!) {
     my $name := $id.&id;
-    my @segments = RakuAST::StrLiteral.new($arg);
-    my $args = RakuAST::ArgList.new: RakuAST::QuotedString.new(:@segments);
-
     RakuAST::Regex::Assertion::Named::Args.new(
-        :$name, :$args :$capturing
+        :$name, :$capturing, :$args,
     );
 }
 
+multi sub assertion(Str:D $id, Bool :$capturing = True) {
+    my $name := $id.&id;
+    RakuAST::Regex::Assertion::Named.new(
+        :$name, :$capturing,
+    );
+}
+
+multi sub arg(Str:D $arg) {
+    RakuAST::ArgList.new: RakuAST::StrLiteral.new($arg);
+}
+
+multi sub arg(Int:D $arg) {
+    RakuAST::ArgList.new: RakuAST::IntLiteral.new($arg);
+}
+
 sub ws(RakuAST::Regex $r) { RakuAST::Regex::WithWhitespace.new($r) }
 
 sub lit(Str:D $s) { RakuAST::Regex::Literal.new($s) }
@@ -161,12 +171,26 @@ multi sub compile(:@numbers!) {
 }
 
 multi sub compile(Str:D :$op!) {
-    assertion-arg 'op', $op;
+    my $args = ','.&arg;
+    'op'.&assertion(:$args);
 }
 
 multi sub compile(:@alt!)   { alt @alt.map(&compile) }
 multi sub compile(:@seq!)   { seq @seq.map(&compile) }
 multi sub compile(:$group!) { group compile($group) }
 
+multi sub compile(:@required) {
+    my $id = 0;
+    my $atom = alt @required.map: {
+        my $args = ($id++).&arg;
+        my $seen = 'seen'.&assertion(:$args).&look-ahead(:negated);
+        my $term = compile($_);
+        [$term, $seen].&seq;
+    }
+    $atom .= &group;
+    my RakuAST::Regex::Quantifier::Range $quantifier .= new: :min($id), :max($id);
+    RakuAST::Regex::QuantifiedAtom.new: :$atom, :$quantifier;
+}
+
 multi sub compile($arg) { compile |$arg }
 
diff --git a/lib/CSS/Specification/Compiler/Actions.rakumod b/lib/CSS/Specification/Compiler/Actions.rakumod
index 31466fa..621931a 100644
--- a/lib/CSS/Specification/Compiler/Actions.rakumod
+++ b/lib/CSS/Specification/Compiler/Actions.rakumod
@@ -80,16 +80,14 @@ method term-options($/) {
 
 method term-combo($/) {
     my @combo = @<term>>>.ast;
-
+warn @combo.elems;
     make @combo == 1 ?? @combo[0] !! (:@combo)
 }
 
 method term-required($/) {
-    my @choices = $<term>>>.ast;
+    my @required = $<term>>>.ast;
 
-    make @choices == 1
-        ?? @choices[0]
-        !! [~] ('required' => @choices)
+    make @required == 1 ?? @required[0] !! (:@required);
 }
 
 method term-seq($/) {
@@ -134,7 +132,8 @@ method value:sym<func>($/) is DEPRECATED {
 }
 
 method value:sym<keywords>($/) {
-    make 'keywords' => @<keyw>.map: {.ast.value};
+    my @keywords = @<keyw>.map: {.ast.value};
+    make (:@keywords);
 }
 
 method value:sym<keyw-quant>($/) {
diff --git a/t/00compile.t b/t/00compile.t
index abfc916..b702719 100644
--- a/t/00compile.t
+++ b/t/00compile.t
@@ -73,11 +73,13 @@ for (
         deparse => '<length>** 1..4% <op(",")>',
     },
 ##    # precedence tests taken from: https://developer.mozilla.org/en-US/docs/CSS/Value_definition_syntax
-##    'spec' => {input => 'bold thin && <length>',
-##               deparse => ':my @*SEEN; [ bold & <keyw> thin & <keyw> <!seen(0)> | <length> <!seen(1)> ]**2',
-##    },
+    'spec' => {
+        input => 'bold thin && <length>',
+        ast => :required[:seq[:keywords["bold"], :keywords["thin"]], :rule("length")],
+        deparse => ':my @S; [ bold & <keyw> thin & <keyw> <!{@S[0]++}> | <length>  <!{@S[1]++}> ]**2',
+    },
 ##    'spec' => {input => 'bold || thin && <length>',
-##               deparse => ':my @*SEEN; [ bold & <keyw> <!seen(2)> | [ thin & <keyw> <!seen(0)> | <length> <!seen(1)> ]**2 <!seen(3)> ]+',
+##               deparse => ':my @S; [ bold & <keyw> <!{@S[2]++}> | [ thin & <keyw> <!{@S[0]++}> | <length> <!{@S[1]++}> ]**2 <!{@S[3]++}> ]+',
 ##    },
 ##    'property-spec' => {input => "'content'\tnormal | none | [ <string> | <uri> | <counter> | attr(<identifier>) | open-quote | close-quote | no-open-quote | no-close-quote ]+ | inherit	normal	:before and :after pseudo-elements	no",
 ##                        ast => {:props['content'],
diff --git a/t/build.t b/t/build.t
index 51a3a18..8b78ae9 100644
--- a/t/build.t
+++ b/t/build.t
@@ -33,9 +33,11 @@ capture({
 }, 't/lib/Test/CSS/Aural/Spec/Actions.rakumod');
 lives-ok {require ::($actions-name)}, "$actions-name compilation";
 
-my RakuAST::Package $interface-package = CSS::Specification::Build::generate( 'interface', @role-id, :$input-path );
-'t/lib/Test/CSS/Aural/Spec/Interface.rakumod'.IO.spurt: $interface-package.DEPARSE;
 my $role-name = @role-id.join: '::';
+
+capture({
+    CSS::Specification::Build::generate( 'interface', $role-name, :$input-path );
+}, 't/lib/Test/CSS/Aural/Spec/Interface.rakumod');
 lives-ok {require ::($role-name)}, "$role-name compilation";
 
 dies-ok {require ::("Test::CSS::Aural::BadGrammar")}, 'grammar composition, unimplemented interface - dies';
diff --git a/t/lib/Test/CSS/Aural/Spec/Interface.rakumod b/t/lib/Test/CSS/Aural/Spec/Interface.rakumod
index 94c68f5..1b301c8 100644
--- a/t/lib/Test/CSS/Aural/Spec/Interface.rakumod
+++ b/t/lib/Test/CSS/Aural/Spec/Interface.rakumod
@@ -1,35 +1,16 @@
-role Test::CSS::Aural::Spec::Interface {
-    method angle ($/) {
-        ...
-    }
-    method color ($/) {
-        ...
-    }
-    method frequency ($/) {
-        ...
-    }
-    method generic-voice ($/) {
-        ...
-    }
-    method identifier ($/) {
-        ...
-    }
-    method number ($/) {
-        ...
-    }
-    method percentage ($/) {
-        ...
-    }
-    method specific-voice ($/) {
-        ...
-    }
-    method string ($/) {
-        ...
-    }
-    method time ($/) {
-        ...
-    }
-    method uri ($/) {
-        ...
-    }
-}
\ No newline at end of file
+use v6;
+#  -- DO NOT EDIT --
+# generated by: t/build.t
+unit role Test::CSS::Aural::Spec::Interface;
+
+method angle($/) { ... }
+method color($/) { ... }
+method frequency($/) { ... }
+method generic-voice($/) { ... }
+method identifier($/) { ... }
+method number($/) { ... }
+method percentage($/) { ... }
+method specific-voice($/) { ... }
+method string($/) { ... }
+method time($/) { ... }
+method uri($/) { ... }