Documentation

upper aka up — convert to uppercase a string
lower aka low — convert to lowercase a string
date_format - format date, timestamp via strftime() function
date - format date, timestamp via date() function
truncate — truncate thee string to specified length
escape aka e — escape the string
unescape — unescape the string
strip — remove extra whitespaces
length — calculate length of string, array, object
in — find value in string or array
match — match string against a pattern.
ematch — perform a regular expression match.
replace — replace all occurrences of the search string with the replacement string.
ereplace — perform a regular expression search and replace.
split — split a string by string.
esplit — split string by a regular expression.
join — join array elements with a string.
allowed functions: json_encode, json_decode, count, is_string, is_array, is_numeric, is_int, is_object, strtotime, gettype, is_double, ip2long, long2ip, strip_tags, nl2br
or add yours

Arithmetic operators — +, -, *, /, %
Logical operators — ||, &&, !$var, and, or, xor
Comparison operators — >, >=, <, <=, ==, !=, !==, <>
Bitwise operators — |, &, ^, ~$var, >>, <<
Assignment operators — =, +=, -=, *=, /=, %=, &=, |=, ^=, >>=, <<=
String concatenation operators — $str1 ~ $str2, $str1 ~~ $str2, $str1 ~= $str2
Ternary operators — $a ? $b : $c, $a ! $b : $c, $a ?: $c, $a !: $c
Check operators — $var?, $var!
Test operator — is, is not
Containment operator — in, not in