diff --git a/src/rust/cli/cmn.rs b/src/rust/cli/cmn.rs
index 6d290cd2cdb..a051b267dbd 100644
--- a/src/rust/cli/cmn.rs
+++ b/src/rust/cli/cmn.rs
@@ -8,11 +8,32 @@ use std::io;
 use std::fmt;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
-
+use std::string::ToString;
 use std::io::{Write, Read, stdout};
 
 use std::default::Default;
 
+const FIELD_SEP: &'static str = ".";
+
+#[derive(Clone, Default)]
+pub struct FieldCursor(Vec<String>);
+
+impl ToString for  FieldCursor {
+    fn to_string(&self) -> String {
+        String::new()
+    }
+}
+
+impl FieldCursor {
+    pub fn set(&mut self, value: &str) -> Result<(), CLIError> {
+        Ok(())
+    }
+
+    pub fn num_fields(&self) -> usize {
+        self.0.len()
+    }
+}
+
 pub fn parse_kv_arg<'a>(kv: &'a str, err: &mut InvalidOptionsError)
                                                                         -> (&'a str, Option<&'a str>) {
     let mut add_err = || err.issues.push(CLIError::InvalidKeyValueSyntax(kv.to_string()));
diff --git a/src/rust/lib.rs b/src/rust/lib.rs
index e05f416047f..3893c42eed8 100644
--- a/src/rust/lib.rs
+++ b/src/rust/lib.rs
@@ -151,4 +151,44 @@ bar\r\n\
         assert_eq!(r.0.first, 2);
         assert_eq!(r.0.last, 42);
     }
+}
+
+#[cfg(test)]
+mod test_cli {
+    use super::cli::cmn::*;
+
+    use std::default::Default;
+
+    #[test]
+    fn cursor() {
+        let mut c: FieldCursor = Default::default();
+
+        assert_eq!(c.to_string(), "");
+        assert_eq!(c.num_fields(), 0);
+        assert!(c.set(".").is_ok());
+        assert!(c.set("..").is_err());
+        assert_eq!(c.num_fields(), 0);
+
+        assert!(c.set("foo").is_ok());
+        assert_eq!(c.to_string(), "foo");
+        assert_eq!(c.num_fields(), 1);
+        assert!(c.set("..").is_ok());
+        assert_eq!(c.num_fields(), 0);
+        assert_eq!(c.to_string(), "");
+
+        assert!(c.set("foo.").is_err());
+
+        assert!(c.set("foo.bar").is_ok());
+        assert_eq!(c.num_fields(), 2);
+        assert_eq!(c.to_string(), "foo.bar");
+        assert!(c.set("sub.level").is_ok());
+        assert_eq!(c.num_fields(), 4);
+        assert_eq!(c.to_string(), "foo.bar.sub.level");
+        assert!(c.set("...other").is_ok());
+        assert_eq!(c.to_string(), "foo.bar.other");
+        assert_eq!(c.num_fields(), 3);
+        assert!(c.set(".one.two.three...beer").is_ok());
+        assert_eq!(c.num_fields(), 2);
+        assert_eq!(c.to_string(), "one.beer");
+    }
 }
\ No newline at end of file