diff --git a/lib/interscript/isc/document_builder.rb b/lib/interscript/isc/document_builder.rb
index d6983368..886778b6 100644
--- a/lib/interscript/isc/document_builder.rb
+++ b/lib/interscript/isc/document_builder.rb
@@ -263,7 +263,9 @@ def extract_stage_items(n)
         elsif n[:compose]
           [{kind: :compose}]
         elsif n[:case]
-          [{kind: :string_case, op: n[:case].to_s}]
+          item = {kind: :string_case, op: n[:case].to_s}
+          item[:kwargs] = extract_kwargs(n[:case_kwargs]) if n[:case_kwargs]
+          [item]
         elsif n[:funcall_name]
           [{kind: :funcall, name: n[:funcall_name].to_s, kwargs: extract_kwargs(n[:funcall_kwargs])}]
         elsif n[:dep]
diff --git a/lib/interscript/isc/generator.rb b/lib/interscript/isc/generator.rb
index 1505afce..655abc4e 100644
--- a/lib/interscript/isc/generator.rb
+++ b/lib/interscript/isc/generator.rb
@@ -96,12 +96,25 @@ def run_target(run)
       end
 
       def funcall(rule, pad)
-        unless rule.kwargs.empty?
-          raise UnsupportedConstruct,
-            "cannot generate #{rule.name}(...) with kwargs as ISC"
-        end
+        case rule.name
+        when :separate
+          separator = rule.kwargs[:separator]
+          return "#{pad}separate\n" if separator.nil?
+
+          "#{pad}separate separator #{item(separator)}\n"
+        when :title_case
+          word_separator = rule.kwargs[:word_separator]
+          return "#{pad}title_case\n" if word_separator.nil?
 
-        "#{pad}#{rule.name}\n"
+          "#{pad}title_case word_separator: #{quote(word_separator)}\n"
+        else
+          unless rule.kwargs.empty?
+            raise UnsupportedConstruct,
+              "cannot generate #{rule.name}(...) with kwargs as ISC"
+          end
+
+          "#{pad}#{rule.name}\n"
+        end
       end
 
       # -- items --
diff --git a/lib/interscript/isc/grammar/concerns/stages.rb b/lib/interscript/isc/grammar/concerns/stages.rb
index 3cdb4983..5838a386 100644
--- a/lib/interscript/isc/grammar/concerns/stages.rb
+++ b/lib/interscript/isc/grammar/concerns/stages.rb
@@ -54,8 +54,11 @@ module Stages
           end
 
           # `downcase`, `upcase`, `title_case` — string-case directives.
+          # title_case takes an optional word_separator kwarg.
           rule(:string_case_directive) do
-            (str("downcase") | str("upcase") | str("title_case")).as(:case)
+            (str("downcase") | str("upcase")).as(:case) |
+              (str("title_case").as(:case) >>
+                (whitespace >> kwarg_list.as(:case_kwargs)).maybe)
           end
 
           # `compose` / `decompose` — Unicode normalization directives.
diff --git a/lib/interscript/isc/node_adapter.rb b/lib/interscript/isc/node_adapter.rb
index df6c0a56..8786c2a1 100644
--- a/lib/interscript/isc/node_adapter.rb
+++ b/lib/interscript/isc/node_adapter.rb
@@ -111,12 +111,12 @@ def build_stage(stage_def)
           when :run
             stage.children << build_run_rule(item)
           when :separate
-            stage.children << Interscript::Node::Rule::Sub.new(
-              Interscript::Node::Item::String.new(" "),
-              Interscript::Node::Item::String.new(item[:separator]&.value || "-")
-            )
+            kwargs = {}
+            kwargs[:separator] = item[:separator].value if item[:separator]
+            stage.children << Interscript::Node::Rule::Funcall.new(:separate, **kwargs)
           when :string_case
-            stage.children << Interscript::Node::Rule::Funcall.new(item[:op].to_sym)
+            stage.children << Interscript::Node::Rule::Funcall.new(item[:op].to_sym,
+              **(item[:kwargs] || {}).transform_keys(&:to_sym))
           when :compose
             stage.children << Interscript::Node::Rule::Funcall.new(:compose)
           when :decompose
diff --git a/spec/interscript/isc/generator_spec.rb b/spec/interscript/isc/generator_spec.rb
index be8e0532..9e820de9 100644
--- a/spec/interscript/isc/generator_spec.rb
+++ b/spec/interscript/isc/generator_spec.rb
@@ -86,6 +86,29 @@ def round_trip_stage(&block)
     expect(reparsed.call("ava eve")).to eq(original.call("ava eve"))
   end
 
+  it "round-trips separate and title_case directives" do
+    original = document {
+      stage {
+        title_case
+        separate
+      }
+    }
+    reparsed = round_trip(original)
+    expect(reparsed.call("hello world")).to eq(original.call("hello world"))
+
+    kwargs_doc = document {
+      stage {
+        title_case word_separator: ""
+        separate separator: "|"
+      }
+    }
+    kwargs_reparsed = round_trip(kwargs_doc)
+    expect(kwargs_reparsed.call("hello world hello hello")).to eq(
+      kwargs_doc.call("hello world hello hello")
+    )
+    expect(kwargs_reparsed.call("こんいちは")).to eq(kwargs_doc.call("こんいちは"))
+  end
+
   it "round-trips multiple stages with a stage run" do
     original = document {
       stage :first do