Which distinction between tadhyīl and īghāl is sound?

Iṭnāb: Tadhyīl, Takmīl (Iḥtirās), and Tatmīm

• Both must occur at the end of verse
• Īghāl is always a clause, tadhyīl always a single word
• Īghāl relates to the close of verse; tadhyīl is not restricted to it
• Tadhyīl excludes any semantic relation