Add docs for .synth() and .error().

README.rst

@@ -261,9 +261,15 @@ VOID xreader.synth()
 --------------------
 
 Generate a synthetic client response body from the file contents. This
-method may only be called in ``vcl_synth``.
+method may only be called in ``vcl_synth``. Invokes VCL failure if the
+most recent update check encountered an error, or if invoked in any
+other VCL subroutine besides ``vcl_synth``.
 
-XXX ...
+Example::
+
+  sub vcl_synth {
+	synth_body.synth();
+  }
 
 .. _xreader.error():
 
@@ -271,9 +277,14 @@ BOOL xreader.error()
 --------------------
 
 Return true if and only if an error condition was determined the last
-time the file was checked.
+time the file was checked. This is a way to avoid VCL failure in error
+conditions.
 
-XXX ...
+Example::
+
+  if (rdr.error()) {
+	call do_file_error_handling;
+  }
 
 .. _xreader.errmsg():
 

src/vmod_file.vcc

@@ -241,16 +241,27 @@ message.
 $Method VOID .synth()
 
 Generate a synthetic client response body from the file contents. This
-method may only be called in ``vcl_synth``.
+method may only be called in ``vcl_synth``. Invokes VCL failure if the
+most recent update check encountered an error, or if invoked in any
+other VCL subroutine besides ``vcl_synth``.
 
-XXX ...
+Example::
+
+  sub vcl_synth {
+	synth_body.synth();
+  }
 
 $Method BOOL .error()
 
 Return true if and only if an error condition was determined the last
-time the file was checked.
+time the file was checked. This is a way to avoid VCL failure in error
+conditions.
 
-XXX ...
+Example::
+
+  if (rdr.error()) {
+	call do_file_error_handling;
+  }
 
 $Method STRING .errmsg()