dbms_metadata.set_transform_param 'PRETTY' option does not work

I issue these statements:

SQL> execute DBMS_METADATA.SET_TRANSFORM_PARAM(DBMS_METADATA.SESSION_TRANSFORM,'PRETTY',true);

SQL> select dbms_metadata.get_ddl('VIEW','AP_TAX_LINES_SUMMARY_V','APPS') from dual

The output does not look PRETTY at all.

Does it only work with certain object types?  This is the description of the option:

PRETTY (all objects) - If TRUE, format the output with indentation and line feeds.
Defaults to TRUE.

Thanks.