Question: This 2013 independent documentary film focuses on a fretted string instrument of what family?

Context paragraphs:
Bowed dulcimer: The bowed dulcimer is a musical instrument.  Designed in the style of the Appalachian dulcimer (a fretted string instrument of the zither family, typically with three or four strings), it is either a standard instrument played with a violin bow, or a purpose-built dulcimer designed around bow playing.  The purpose-designed instrument is described as resembling a hybrid between a dulcimer and a cello or viola da gamba.

Lute: A lute ( , or ) is any plucked string instrument with a neck (either fretted or unfretted) and a deep round back enclosing a hollow cavity, usually with a sound hole or opening in the body.  More specifically, the term "lute" can refer to an instrument from the family of European lutes.  The term also refers generally to any string instrument having the strings running in a plane parallel to the sound table (in the Hornbostel–Sachs system).  The strings are attached to pegs or posts at the end of the neck, which have some type of turning mechanism to enable the player to tighten the tension on the string or loosen the tension before playing (which respectively raise or lower the pitch of a string), so that each string is tuned to a specific pitch (or note).  The lute is plucked or strummed with one hand while the other hand "frets" (presses down) the strings on the neck's fingerboard.  By pressing the strings on different places of the fingerboard, the player can shorten or lengthen the part of the string that is vibrating, thus producing higher or lower pitches (notes).

Appalachian dulcimer: The Appalachian dulcimer (many variant names; see below) is a fretted string instrument of the zither family, typically with three or four strings, originally played in the Appalachian region of the United States.  The body extends the length of the fingerboard, and its fretting is generally diatonic.

Turkish tambur: The Tambur (spelled in keeping with TDK conventions) is a fretted string instrument of Turkey and the former lands of the Ottoman Empire.  Like the ney, the armudi (lit.  pear-shaped) kemençe and the kudüm, it constitutes one of the four instruments of the basic quartet of Turkish classical music a.k.a. "Türk Sanat Müziği" (lit.  Turkish Artistic Music).  Of the two variants, one is played with a plectrum ("mızraplı tambur") and the other with a bow ("yaylı tambur").  The player is called a "tamburî".

Hearts of the Dulcimer: Hearts of the Dulcimer is a 2013 independent documentary film focusing on the Appalachian dulcimer, and particularly its role in the 1960s California counterculture, through interviews with builders and players of this musical instrument.  The film was written and directed by Patricia Delich and Wayne Jiang.

Kurdish tanbur: Kurdish tanbur (Kurdish: tembûr ته‌مبوور‎ ) or tanbour (Persian: تنبور‎ ‎ ), a fretted string instrument, is an initial and main form of the tanbūr instrument family, original of and unique to the Kurdish people.

Yueqin: The yueqin or yue qin (Chinese: 月琴 ,  "yuèqín"), formerly romanized as yüeh-ch‘in and also known as the moon guitar, moon zither, gekkin, laqin, or la-ch‘in, is a traditional Chinese string instrument.  It is a lute with a round, hollow wooden body which gives it the nickname "moon guitar".  It has a short fretted neck and four strings tuned in courses of two (each pair of strings is tuned to a single pitch), generally tuned to the interval of a perfect fifth.  Occasionally, the body of the yueqin may be octagonal in shape.  It is an important instrument in the Beijing opera orchestra, often taking the role of main melodic instrument in lieu of the bowed string section.  The frets on all Chinese lutes are high so that the fingers never touch the actual body—distinctively different from western fretted instruments.  This allows for a greater control over timbre and intonation than their western counterparts, but makes chordal playing more difficult.

Hammer-on: A hammer-on is a playing technique performed on a stringed instrument (especially on a fretted string instrument, such as a guitar) by sharply bringing a fretting-hand finger down on the fingerboard behind a fret, causing a note to sound.  This technique is the opposite of the pull-off.

Octave mandolin: The octave mandolin is a fretted string instrument with four pairs of strings tuned in fifths, G, D, A, E (low to high), an octave below a mandolin.  It is larger than the mandola, but smaller than the mandocello and its construction is similar to other instruments in the mandolin family.  Usually the courses are all unison pairs but the lower two may sometimes be strung as octave pairs with the higher-pitched octave string on top so that it is hit before the thicker lower-pitched string.  Alternate tunings of G, D, A, D and A, D, A, D are often employed by Celtic musicians.

Cello: The cello ( ; plural cellos or celli) or violoncello ( ; ] ) is a bowed, and sometimes plucked, string instrument with four strings tuned in perfect fifths.  The strings from low to high are generally tuned to C, G, D and A, an octave lower than the viola.  It is the bass member of the violin family of musical instruments, which also includes the violin, viola and the double bass.  The cello is used as a solo musical instrument, as well as in chamber music ensembles (e.g., string quartet), string orchestras, as a member of the string section of symphony orchestras, and some types of rock bands.  It is the second-largest and second lowest (in pitch) bowed string instrument in the modern symphony orchestra, the double bass being the largest and having the lowest (deepest) pitch.

Supporting paragraphs: Hearts of the Dulcimer Appalachian dulcimer
Answer: zither