The alphabetical list of built-ins:
abs
absolute_template_name
ancestors
api
boolean
byte
c
cap_first
capitalize
ceiling
children
chop_linebreak
chunk
contains
counter
date
date_if_unknown
datetime
datetime_if_unknown
default
double
drop_while
ends_with
ensure_ends_with
ensure_starts_with
esc
eval
exists
filter
first
float
floor
groups
has_api
has_content
has_next
html
if_exists
index
index_of
int
interpret
is_boolean
is_collection
is_collection_ex
is_date
is_date_like
is_date_only
is_datetime
is_directive
is_enumerable
is_even_item
is_first
is_hash
is_hash_ex
is_indexable
is_infinite
is_last
is_macro
is_markup_output
is_method
is_nan
is_node
is_number
is_odd_item
is_sequence
is_string
is_time
is_transform
is_unknown_date_like
iso
iso_h
iso_h_nz
iso_local
iso_local_h
iso_local_h_nz
iso_local_m
iso_local_m_nz
iso_local_ms
iso_local_ms_nz
iso_local_nz
iso_m
iso_m_nz
iso_ms
iso_ms_nz
iso_nz
iso_utc
iso_utc_fz
iso_utc_h
iso_utc_h_nz
iso_utc_m
iso_utc_m_nz
iso_utc_ms
iso_utc_ms_nz
iso_utc_nz
item_cycle
item_parity
item_parity_cap
j_string
join
js_string
json_string
keep_after
keep_after_last
keep_before
keep_before_last
keys
last
last_index_of
left_pad
length
long
lower_abc
lower_case
map
markup_string
matches
max
min
namespace
new
next_sibling
no_esc
node_name
node_namespace
node_type
number
number_to_date
number_to_datetime
number_to_time
parent
previous_sibling
remove_beginning
remove_ending
replace
reverse
right_pad
root
round
rtf
seq_contains
seq_index_of
seq_last_index_of
sequence
short
size
sort
sort_by
split
starts_with
string
substring
switch
take_while
then
time
time_if_unknown
trim
truncate
truncate_c
truncate_c_m
truncate_m
truncate_w
truncate_w_m
uncap_first
upper_abc
upper_case
url
url_path
values
web_safe
with_args
with_args_last
word_list
xhtml
xml