### 3.3.3 Engravers explained

Every mark on the printed output of a score produced by LilyPond is produced by an `Engraver`. Thus there is an engraver to print staves, one to print note heads, one for stems, one for beams, etc, etc. In total there are over 120 such engravers! Fortunately, for most scores it is not necessary to know about more than a few, and for simple scores you do not need to know about any.

Engravers live and operate in Contexts. Engravers such as the `Metronome_mark_engraver`, whose action and output apply to the score as a whole, operate in the highest level context – the `Score` context.

The `Clef_engraver` and `Key_engraver` are to be found in every `Staff` Context, as different staves may require different clefs and keys.

The `Note_heads_engraver` and `Stem_engraver` live in every `Voice` context, the lowest level context of all.

Each engraver processes the particular objects associated with its function, and maintains the properties that relate to that function. These properties, like the properties associated with contexts, may be modified to change the operation of the engraver or the appearance of those elements in the printed score.

Engravers all have compound names formed from words which describe their function. Just the first word is capitalized, and the remainder are joined to it with underscores. Thus the `Staff_symbol_engraver` is responsible for creating the lines of the staff, the `Clef_engraver` determines and sets the pitch reference point on the staff by drawing a clef symbol.

Here are some of the most common engravers together with their function. You will see it is usually easy to guess the function from the name, or vice versa.

Engraver | Function
--- | ---
Accidental_engraver | Makes accidentals, cautionary and suggested accidentals
Beam_engraver | Engraves beams
Clef_engraver | Engraves clefs
Completion_heads_engraver | Splits notes which cross bar lines
Dynamic_engraver | Creates hairpins and dynamic texts
Forbid_line_break_engraver | Prevents line breaks if a musical element is still active
Key_engraver | Creates the key signature
Metronome_mark_engraver | Engraves metronome marking
Note_heads_engraver | Engraves note heads
Rest_engraver | Engraves rests
Staff_symbol_engraver | Engraves the five (by default) lines of the staff
Stem_engraver | Creates stems and single-stem tremolos
Time_signature_engraver | Creates time signatures

We shall see later how the output of LilyPond can be changed by modifying the action of Engravers.

#### See also

Internals reference: Engravers and Performers.

其他语言：česky, deutsch, español, français, magyar, italiano, 日本語, nederlands。
About automatic language selection.

#### LilyPond — Learning Manual v2.18.2 (稳定分支).