The jcs:print() function emits formatted output text. The text appears in the CLI. Most standard printf formats are supported, in addition to some JUNOS software-specific ones. The %j1 operator emits the field only if the field was changed from the last time the function was run. The %jc operator capitalizes the first letter of the format output. The %jt{TAG} operator emits the tag if the field is not empty.
<xsl:value-of select="jcs:printf('%-24j1s %-5jcs %-5jcs %s%jt{ --> }s\n',
'so-0/0/0', 'up', 'down', '10.1.2.3', '')"/>