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The wrap and anchor options are implemented via the Output Filters. The others are handled during interpretation by ST. Well, the filters also are notified that a separator vs regular string is coming out to prevent newlines between real elements and separators.

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Java examples

Here is an example use of the format option.

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public void testRendererWithFormatAndSeparatorAndNull() throws Exception {
    StringTemplate st =new StringTemplate(
        "The names: <names; separator=\" and \", null=\"n/a\", format=\"upper\">",
        AngleBracketTemplateLexer.class);
    List names = new ArrayList();
    names.add("ter");
    names.add(null);
    names.add("sriram");
    st.setAttribute("names", names);
    st.registerRenderer(String.class, new StringRenderer());
    String expecting = "The names: TER and N/A and SRIRAM";
    String result = st.toString();
    assertEquals(expecting, result);
}

Python examples

If you are constructing HTML documents you have to escape plain text strings so that < or & characters appear as literal text and do not act as HTML delimiters (thus opening a wide range of possible attacks if the text originated from user input).

import cgi
import stringtemplate3

group = stringtemplate3.StringTemplateGroup(
    name="default", rootDir="path/to/templates/"
    )

class EscapeRenderer(stringtemplate3.AttributeRenderer):
    def toString(self, o, formatName=None):
        if formatName is None:
            # no formatting specified
            return str(o)

        if formatName == "escape":
            return cgi.escape(str(o))
        else:
            raise ValueError("Unsupported format name")

group.registerRenderer(str, EscapeRenderer())

st = group.getInstanceOf("blogEntry")
st['comment'] = database.loadComment() # an instance with username, text, url, ... attributes

Then you can use $comment.text; format="escape"$ in your templates whenever an attribute is not known to be save.