function string:lstrip()
  if self == nil then
    return nil
    end
  local s = self:gsub("^%s+", "")
  return s
  end
function string:rstrip()
  if self == nil then
    return nil
    end
  local s = self:gsub("%s+$", "")
  return s
  end
function string:strip()
  return self:lstrip():rstrip()
  end
function string:startswith(text)
  local size = text:len()
  if self:sub(1, size) == text then
    return self
    end
  end
function string:endswith(text)
  if self:sub(-#text) == text then
    return self
    end
  end
