diff --git a/include/modules/meta/base.inl b/include/modules/meta/base.inl
index 8fd82e1a..35ea373d 100644
--- a/include/modules/meta/base.inl
+++ b/include/modules/meta/base.inl
@@ -137,13 +137,13 @@ namespace modules {
         if (tag_built)
           i++;
       } else if (is_blankspace && tag_built) {
-        m_builder->node(" ");
+        m_builder->space(1_z);
       } else if (!is_blankspace) {
         m_builder->node(tag);
       }
     }
 
-    return format->decorate(m_builder.get(), m_builder->flush());
+    return format->decorate(&*m_builder, m_builder->flush());
   }
 
   // }}}
diff --git a/src/components/builder.cpp b/src/components/builder.cpp
index 54c0e5a4..af2a4ee1 100644
--- a/src/components/builder.cpp
+++ b/src/components/builder.cpp
@@ -13,12 +13,12 @@ POLYBAR_NS
 #endif
 
 builder::builder(const bar_settings bar) : m_bar(bar) {
-  m_tags[syntaxtag::A] = 1;
-  m_tags[syntaxtag::B] = 2;
-  m_tags[syntaxtag::F] = 3;
-  m_tags[syntaxtag::T] = 9;
-  m_tags[syntaxtag::o] = 7;
-  m_tags[syntaxtag::u] = 8;
+  m_tags[syntaxtag::A] = 0;
+  m_tags[syntaxtag::B] = 0;
+  m_tags[syntaxtag::F] = 0;
+  m_tags[syntaxtag::T] = 0;
+  m_tags[syntaxtag::o] = 0;
+  m_tags[syntaxtag::u] = 0;
 
   m_colors[syntaxtag::B] = string();
   m_colors[syntaxtag::F] = string();
@@ -58,7 +58,7 @@ string builder::flush() {
     cmd_close();
   }
 
-  string output = m_output.data();
+  string output{m_output};
 
   // reset values
   m_tags.clear();
@@ -66,7 +66,7 @@ string builder::flush() {
   m_output.clear();
   m_fontindex = 1;
 
-  return string_util::replace_all(output, string{BUILDER_SPACE_TOKEN}, " ");
+  return string_util::replace_all(output, BUILDER_SPACE_TOKEN, " ");
 }
 
 /**
diff --git a/src/modules/meta/base.cpp b/src/modules/meta/base.cpp
index c24237a8..46f4d335 100644
--- a/src/modules/meta/base.cpp
+++ b/src/modules/meta/base.cpp
@@ -10,6 +10,11 @@ namespace modules {
   // module_format {{{
 
   string module_format::decorate(builder* builder, string output) {
+    if (output.empty()) {
+      builder->flush();
+      return "";
+    }
+
     if (offset != 0) {
       builder->offset(offset);
     }
@@ -64,17 +69,19 @@ namespace modules {
   // module_formatter {{{
 
   void module_formatter::add(string name, string fallback, vector<string>&& tags, vector<string>&& whitelist) {
+    using namespace std::string_literals;
+
     auto format = make_unique<module_format>();
 
     format->value = m_conf.get<string>(m_modname, name, move(fallback));
-    format->fg = m_conf.get<string>(m_modname, name + "-foreground", "");
-    format->bg = m_conf.get<string>(m_modname, name + "-background", "");
-    format->ul = m_conf.get<string>(m_modname, name + "-underline", "");
-    format->ol = m_conf.get<string>(m_modname, name + "-overline", "");
-    format->spacing = m_conf.get<int>(m_modname, name + "-spacing", DEFAULT_SPACING);
-    format->padding = m_conf.get<int>(m_modname, name + "-padding", 0);
-    format->margin = m_conf.get<int>(m_modname, name + "-margin", 0);
-    format->offset = m_conf.get<int>(m_modname, name + "-offset", 0);
+    format->fg = m_conf.get(m_modname, name + "-foreground", ""s);
+    format->bg = m_conf.get(m_modname, name + "-background", ""s);
+    format->ul = m_conf.get(m_modname, name + "-underline", ""s);
+    format->ol = m_conf.get(m_modname, name + "-overline", ""s);
+    format->spacing = m_conf.get(m_modname, name + "-spacing", 0_z);
+    format->padding = m_conf.get(m_modname, name + "-padding", 0_z);
+    format->margin = m_conf.get(m_modname, name + "-margin", 0_z);
+    format->offset = m_conf.get(m_modname, name + "-offset", 0_z);
     format->tags.swap(tags);
 
     try {
@@ -92,17 +99,16 @@ namespace modules {
     for (auto&& tag : string_util::split(format->value, ' ')) {
       if (tag[0] != '<' || tag[tag.length() - 1] != '>') {
         continue;
-      }
-      if (find(format->tags.begin(), format->tags.end(), tag) != format->tags.end()) {
+      } else if (find(format->tags.begin(), format->tags.end(), tag) != format->tags.end()) {
         continue;
-      }
-      if (find(whitelist.begin(), whitelist.end(), tag) != whitelist.end()) {
+      } else if (find(whitelist.begin(), whitelist.end(), tag) != whitelist.end()) {
         continue;
+      } else {
+        throw undefined_format_tag(tag + " is not a valid format tag for \""+ name +"\"");
       }
-      throw undefined_format_tag("[" + m_modname + "] Undefined \"" + name + "\" tag: " + tag);
     }
 
-    m_formats.insert(make_pair(name, move(format)));
+    m_formats.insert(make_pair(move(name), move(format)));
   }
 
   bool module_formatter::has(const string& tag, const string& format_name) {
diff --git a/src/modules/xwindow.cpp b/src/modules/xwindow.cpp
index 8e998cd4..4f11a84d 100644
--- a/src/modules/xwindow.cpp
+++ b/src/modules/xwindow.cpp
@@ -125,13 +125,11 @@ namespace modules {
    * Output content as defined in the config
    */
   bool xwindow_module::build(builder* builder, const string& tag) const {
-    if (tag == TAG_LABEL) {
+    if (tag == TAG_LABEL && m_label && m_label.get()) {
       builder->node(m_label);
-    } else {
-      return false;
+      return true;
     }
-
-    return true;
+    return false;
   }
 }