7.5a As first syllable of word.

The contractions for be, con, and dis are used only when they constitute a syllable and occur at the beginning of a word or at the beginning of a line in a divided word. Thus, these contractions are used in such words as believe, conduct, and district. They are not used in words such as unbelievable, misconduct, or predisposed where they do not occur at the beginning of the word. Nor are they used in such words as belligerent, conch, and disc where other letters are included in the syllable; or in coniferous and disheveled where all the letters do not fall in the same syllable.

Although, as mentioned above, these contractions cannot be used in the middle of a word that is located all on one line, they are used when the letters of the contraction fall at the beginning of a line in a divided word. Examples:

inconsiderate in-
considerate
disobedient diso-
bedient
-