code: def char2hex(a):
      """Converts a hex character to its integer value.
      '0' becomes 0, '9' becomes 9
      'A' becomes 10, 'F' becomes 15
      'a' becomes 10, 'f' becomes 15
  
      Returns -1 on error."""
      if 48 <= a <= 57:  # 0-9
          return a - 48
      elif 65 <= a <= 70:  # A-F
          return a - 55
      elif 97 <= a <= 102:  # a-f
          return a - 87
      return -1
  
imports: import json
  from ..error import GraphQLSyntaxError
label_desc: Use image node_id 11 for calling a global function with example usage: char2hex(a) and returns: unknown, unknown, unknown, unknown