The official Jenkins documentation only mentions single line commands like the following:
// Declarative //
and (see)
pipeline {
/* insert Declarative Pipeline here */
}
The syntax of the Jenkinsfile is based on Groovy so it is also possible to use groovy syntax for comments. Quote:
/* a standalone multiline comment
spanning two lines */
println "hello" /* a multiline comment starting
at the end of a statement */
println 1 /* one */ + 2 /* two */
or
/**
* such a nice comment
*/