diff --git a/reference/outcontrol/functions/ob-get-status.xml b/reference/outcontrol/functions/ob-get-status.xml
index 20b8ab88b937..687002bcc47f 100644
--- a/reference/outcontrol/functions/ob-get-status.xml
+++ b/reference/outcontrol/functions/ob-get-status.xml
@@ -107,7 +107,14 @@
     <seglistitem>
      <seg>buffer_size</seg>
      <seg>
-      Output buffer size in bytes
+      Currently allocated size of the output buffer in bytes.
+      It starts at <literal>16384</literal> bytes with the default
+      <parameter>chunk_size</parameter>, or at
+      <parameter>chunk_size</parameter> rounded up to the next multiple of
+      <literal>4096</literal> when one is given, and grows in multiples of
+      <literal>4096</literal> as more output is buffered.
+      This is not the amount of data in the buffer (see
+      <literal>buffer_used</literal>).
      </seg>
     </seglistitem>
     <seglistitem>
diff --git a/reference/outcontrol/functions/ob-start.xml b/reference/outcontrol/functions/ob-start.xml
index 1239b0cc0b58..d50a84aca340 100644
--- a/reference/outcontrol/functions/ob-start.xml
+++ b/reference/outcontrol/functions/ob-start.xml
@@ -111,15 +111,22 @@
     <varlistentry>
      <term><parameter>chunk_size</parameter></term>
      <listitem>
-      <para>
+      <simpara>
        If the optional parameter <parameter>chunk_size</parameter> is passed,
        the buffer will be flushed after any block of code resulting in output
        that causes the buffer's length to equal
        or exceed <parameter>chunk_size</parameter>.
        The default value <literal>0</literal> means
        that all output is buffered until the buffer is turned off.
+       A value of <literal>1</literal> means the buffer will be flushed
+       after every output operation, effectively disabling buffering.
+       <parameter>chunk_size</parameter> also determines the initial size of
+       the buffer reported by <function>ob_get_status</function>:
+       <literal>16384</literal> bytes when it is <literal>0</literal>, and
+       <parameter>chunk_size</parameter> rounded up to the next multiple of
+       <literal>4096</literal> otherwise.
        See <xref linkend="outcontrol.buffer-size"/> for more details.
-      </para>
+      </simpara>
      </listitem>
     </varlistentry>
     <varlistentry>