diff --git a/src/api/registry.rs b/src/api/registry.rs
new file mode 100644
index 00000000..c2bcc28e
--- /dev/null
+++ b/src/api/registry.rs
@@ -0,0 +1,91 @@
+use crate::api::schema::*;
+
+use failure::*;
+use std::collections::HashMap;
+use std::sync::Arc;
+
+pub struct Registry {
+    formats: HashMap<&'static str, Arc<ApiStringFormat>>,
+    options: HashMap<&'static str, Arc<Schema>>,
+}
+
+impl Registry {
+
+    pub fn new() -> Self {
+
+        let mut me = Self {
+            formats: HashMap::new(),
+            options: HashMap::new(),
+        };
+
+        me.initialize_formats();
+
+        me.initialize_options();
+
+        me
+    }
+
+    pub fn register_format(&mut self, name: &'static str, format: ApiStringFormat) {
+
+        if let Some(format) = self.formats.get(name) {
+            panic!("standard format '{}' already registered.", name); // fixme: really panic?
+        }
+
+        self.formats.insert(name, Arc::new(format));
+    }
+
+    pub fn lookup_format(&self, name: &str) -> Option<Arc<ApiStringFormat>> {
+
+        if let Some(format) = self.formats.get(name) {
+            return Some(format.clone());
+        }
+        None
+    }
+
+    pub fn register_option(&mut self, name: &'static str, schema: Schema) {
+
+        if let Some(schema) = self.options.get(name) {
+            panic!("standard option '{}' already registered.", name); // fixme: really panic?
+        }
+
+        self.options.insert(name, Arc::new(schema));
+    }
+
+    pub fn lookup_option(&self, name: &str) -> Option<Arc<Schema>> {
+
+        if let Some(schema) = self.options.get(name) {
+            return Some(schema.clone());
+        }
+        None
+    }
+
+    fn initialize_formats(&mut self) {
+
+        self.register_format("pve-node", ApiStringFormat::VerifyFn(verify_pve_node));
+
+    }
+
+    fn initialize_options(&mut self) {
+
+        self.register_option(
+            "pve-vmid",
+            Integer!{
+                description => "The (unique) ID of the VM.",
+                minimum => Some(1),
+                optional => false
+            });
+
+        self.register_option(
+            "pve-node",
+            ApiString!{
+                description => "The cluster node name.",
+                format => self.lookup_format("pve-node")
+            });
+     }
+
+}
+
+fn verify_pve_node(value: &str) -> Result<(), Error> {
+
+    Ok(())
+}
diff --git a/src/api/schema.rs b/src/api/schema.rs
index c4319260..2f8f6409 100644
--- a/src/api/schema.rs
+++ b/src/api/schema.rs
@@ -61,7 +61,7 @@ pub struct StringSchema {
     pub default: Option<&'static str>,
     pub min_length: Option<usize>,
     pub max_length: Option<usize>,
-    pub format: ApiStringFormat,
+    pub format: Option<Arc<ApiStringFormat>>,
 }
 
 #[derive(Debug)]
@@ -123,15 +123,33 @@ pub const DEFAULTSTRING: StringSchema = StringSchema {
     default: None,
     min_length: None,
     max_length: None,
-    format: ApiStringFormat::None,
+    format: None,
 };
 
-#[derive(Debug)]
 pub enum ApiStringFormat {
-    None,
     Enum(Vec<String>),
     Pattern(Box<Regex>),
     Complex(Arc<Schema>),
+    VerifyFn(fn(&str) -> Result<(), Error>),
+}
+
+impl std::fmt::Debug for ApiStringFormat {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ApiStringFormat::VerifyFn(fnptr) => {
+                write!(f, "VerifyFn({:p}", fnptr)
+            }
+            ApiStringFormat::Enum(strvec) => {
+                write!(f, "Enum({:?}", strvec)
+            }
+            ApiStringFormat::Pattern(regex) => {
+                write!(f, "Pattern({:?}", regex)
+            }
+            ApiStringFormat::Complex(schema) => {
+                write!(f, "Complex({:?}", schema)
+            }
+        }
+    }
 }
 
 #[macro_export]
@@ -219,20 +237,24 @@ fn parse_simple_value(value_str: &str, schema: &Schema) -> Result<Value, Error>
                 }
             }
 
-            match string_schema.format {
-                ApiStringFormat::None => { /* do nothing */ }
-                ApiStringFormat::Pattern(ref regex) => {
-                    if !regex.is_match(&res) {
-                        bail!("value does not match the regex pattern");
+            if let Some(ref format) = string_schema.format {
+                match format.as_ref() {
+                    ApiStringFormat::Pattern(ref regex) => {
+                        if !regex.is_match(&res) {
+                            bail!("value does not match the regex pattern");
+                        }
                     }
-                }
-                ApiStringFormat::Enum(ref stringvec) => {
-                    if stringvec.iter().find(|&e| *e == res) == None {
-                        bail!("value is not defined in the enumeration.");
+                    ApiStringFormat::Enum(ref stringvec) => {
+                        if stringvec.iter().find(|&e| *e == res) == None {
+                            bail!("value is not defined in the enumeration.");
+                        }
+                    }
+                    ApiStringFormat::Complex(ref _subschema) => {
+                        bail!("implement me!");
+                    }
+                    ApiStringFormat::VerifyFn(verify_fn) => {
+                        verify_fn(&res)?;
                     }
-                }
-                ApiStringFormat::Complex(ref _subschema) => {
-                    bail!("implement me!");
                 }
             }
 
@@ -390,7 +412,7 @@ fn test_query_string() {
 
     let schema = parameter!{name => Arc::new(ApiString!{
         optional => false,
-        format => ApiStringFormat::Pattern(Box::new(Regex::new("test").unwrap()))
+        format => Some(Arc::new(ApiStringFormat::Pattern(Box::new(Regex::new("test").unwrap()))))
     })};
 
     let res = parse_query_string("name=abcd", &schema, true);
@@ -401,7 +423,7 @@ fn test_query_string() {
 
     let schema = parameter!{name => Arc::new(ApiString!{
         optional => false,
-        format => ApiStringFormat::Pattern(Box::new(Regex::new("^test$").unwrap()))
+        format => Some(Arc::new(ApiStringFormat::Pattern(Box::new(Regex::new("^test$").unwrap()))))
     })};
 
     let res = parse_query_string("name=ateststring", &schema, true);
@@ -414,7 +436,7 @@ fn test_query_string() {
 
     let schema = parameter!{name => Arc::new(ApiString!{
         optional => false,
-        format => ApiStringFormat::Enum(vec!["ev1".into(), "ev2".into()])
+        format => Some(Arc::new(ApiStringFormat::Enum(vec!["ev1".into(), "ev2".into()])))
     })};
 
     let res = parse_query_string("name=noenum", &schema, true);
diff --git a/src/lib.rs b/src/lib.rs
index 8dd39e4b..3ebf84fc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,6 +5,7 @@ pub mod api {
 
     #[macro_use]
     pub mod schema;
+    pub mod registry;
     #[macro_use]
     pub mod router;
     pub mod config;
diff --git a/src/main.rs b/src/main.rs
index 9c97bfde..073b40ca 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,8 +20,10 @@ use hyper;
 fn main() {
     println!("Proxmox REST Server example.");
 
+    let prop = Arc::new(ApiString!{ optional => true });
     let schema = parameter!{
-        name => Arc::new(ApiString!{ optional => true })
+        name1 => prop.clone(),
+        name2 => prop.clone()
     };
 
     let args: Vec<String> = std::env::args().skip(1).collect();