The "Unknown:"s below indicate that an entry is incomplete.

• either the entry exist in the language, and please tell.
• either the entry doesn't exist in the language, and please tell so. The entry will be marked as such and won't appear as missing anymore.

• Various

  indentation	block (grouping statements, especially when statements are not expressions)
  ;	commenting (until end of line)
  < > '> '<	comparison
  = '=	equality / inequality (shallow)
  ( ... )	grouping expressions
  XECUTE	runtime evaluation
  case-sensitive: identifiers case-insensitive: commands	tokens (case-sensitivity (keywords, variable identifiers...))
  [a-zA-Z%][a-zA-Z0-9]*	tokens (variable identifier regexp)
  SET v=...	variable assignment or declaration (assignment)
  NEW v	variable assignment or declaration (declaration)

• Control Flow

  goto	breaking control flow (goto (unconditional jump))
  IF c ...	if_then
  $SELECT(c:b1,c2:b2,1:b3)	if_then_else
  IF c ... ELSE ...	if_then_else
  FOR I=10:-1:1 ...	loop (for each value in a numeric range, 1 decrement)
  FOR I=1:1:10 ...	loop (for each value in a numeric range, 1 increment (see also the entries about ranges))
  FOR I=1:2:10 ...	loop (for each value in a numeric range, free increment)

• Strings

  $EXTRACT(s, n)	accessing n-th character
  $CHAR(s)	ascii to character
  $ASCII(s)	character to ascii
  $EXTRACT(s, n, m)	extract a substring
  $FIND	locate a substring
  _	string concatenation
  "..."	strings (with no interpolation of variables)

• Booleans

  0(1)	false value
  '	logical not
  & / !	logical or / and (short circuit)
  anything not false	true value
  1	true value

• Bags and Lists

  $LENGTH

  list size

• Mathematics

  + / - / * / /	addition / subtraction / multiplication / division
  #	modulo (modulo of -3 / 2 is -1)
  -	negation
  same priorities	operator priorities and associativities (addition vs multiplication)
  $RANDOM	random (random number)

Remarks

• (1) beware of 0.0 which is true in Pike!