lib/Assertion.php
function contain($value = null): self {
    if ($this->hasFlag('file')) return $this->expect(@file_get_contents($this->target), stringContains($value));
    return $this->expect($this->target, is_string($this->target) ? stringContains($value) : contains($value));
  }
function contain($value = null): self {
    if ($this->hasFlag('file')) return $this->expect(@file_get_contents($this->target), stringContains($value));
    return $this->expect($this->target, is_string($this->target) ? stringContains($value) : contains($value));
  }
Reports an error if the target does not contain an element or a substring.
@param mixed $value The value to find.
@return self This instance.