diff --git a/src/encoder.rs b/src/encoder.rs
index f9e49cf..66e14c3 100644
--- a/src/encoder.rs
+++ b/src/encoder.rs
@@ -17,7 +17,10 @@ pub trait Encodable {
 
 /// Encoder type, holds a mut ref to a buffer
 /// that it will write data to and an offset
-/// of the next position to write
+/// of the next position to write.
+/// 
+/// This will start writing from the beginning of the buffer, *not* from the end.
+/// The buffer will be grown as needed.
 #[derive(Debug)]
 pub struct Encoder<'a> {
     buffer: &'a mut Vec<u8>,
@@ -35,6 +38,16 @@ impl<'a> Encoder<'a> {
         self.buffer
     }
 
+    /// Returns the slice of the underlying buffer that has been filled.
+    pub fn buffer_filled(&self) -> &[u8] {
+        &self.buffer[..self.offset]
+    }
+
+    /// Returns the number of bytes that have been written to the buffer.
+    pub fn len_filled(&self) -> usize {
+        self.offset
+    }
+
     /// write bytes to buffer
     /// Return:
     ///     number of bytes written