{!-- Supply a default from the template, to output when
  -- tag is not defined.  Everything after the colon :
  -- becomes the tag value (NB: null and undefined are
  -- NOT the same - see example 4 below).
  --}
<p>Hello {$name:there}!  You're our grand prize winner!</p>

Theme theme = new Theme();

// fetch template from themes/example.chtml
Chunk html = theme.makeChunk("example");

// Insert business logic here.
// Normally you write a lot of html.set("this","that") calls here.

StreamWriter out = getStreamWriter();
html.render( out );

///// or, return the rendered template as a string
// return html.toString();

{!-- Default to the empty string, no tag preservation. --}
<div>{$error_message:}</div>

Theme theme = new Theme();

// fetch template from themes/example.chtml
Chunk html = theme.makeChunk("example");

// Insert business logic here.
// Normally you write a lot of html.set("this","that") calls here.

StreamWriter out = getStreamWriter();
html.render( out );

///// or, return the rendered template as a string
// return html.toString();

{!-- Supply a default from the template, to output when
  -- tag is: (A) only whitespace, or (B) is the empty string,
  -- or (C) is not defined at all.
  --
  -- The pipe character | marks the start of a tag output filter.
  --}
Hello {$name|onempty(there)}!  You're our grand prize winner!

Theme theme = new Theme();

// fetch template from themes/example.chtml
Chunk html = theme.makeChunk("example");

// Insert business logic here.
// Normally you write a lot of html.set("this","that") calls here.

StreamWriter out = getStreamWriter();
html.render( out );

///// or, return the rendered template as a string
// return html.toString();

{!-- IMPORTANT!! The following two calls are equivalent:
  --
  --   c.set("tag",null);
  --   c.set("tag","");
  --
  -- Chunk's null-trapping turns null into the empty string.
  -- Furthermore, the empty string is considered "defined" when
  -- rendering the template.
  --
  -- So, if you *want* a default value to display (eg {$tag:default} ),
  -- don't use null!!  Instead, make sure a tag is undefined like so:
  --
  --   c.setOrDelete("tag",null);
  --   // or...
  --   c.unset("tag");
  --   // or just don't call .set() at all!
  --   // in the example below, "tag" will be undefined except on Wed.
  --   if (isWednesday) {
  --     c.set("tag","hump day");
  --   }
  --}
<div>{$tag:default}</div>

Theme theme = new Theme();

// fetch template from themes/example.chtml
Chunk html = theme.makeChunk("example");

// Insert business logic here.
// Normally you write a lot of html.set("this","that") calls here.

StreamWriter out = getStreamWriter();
html.render( out );

///// or, return the rendered template as a string
// return html.toString();