11.1. It is sometimes difficult to render concisely, by means of the in-accord sign, passages containing notes printed with two stems indicating either identical or differing values, and for this purpose special stem signs are used.
11.2. Stem signs are placed after the notes to which they belong, and may not be separated from them by the music hyphen. These signs may be dotted in the same manner as written notes, and they may be modified by the signs in Tables 9, ties; 12, slurs; 17, music parentheses and other variants; and the first seven signs in Table 18, staccatos and accents.
As stem signs may sometimes obscure the melodic line, they should be used with great discretion.