src/Mail/mime.php
function setTXTBody($data, $isfile = false, $append = false)
    {
        if (!$isfile) {
            if (!$append) {
                $this->_txtbody = $data;
            } else {
                $this->_txtbody .= $data;
            }
        } else {
            $cont = $this->_file2str($data);
            if ($this->_isError($cont)) {
                return $cont;
            }
            if (!$append) {
                $this->_txtbody = $cont;
            } else {
                $this->_txtbody .= $cont;
            }
        }

        return true;
    }
function setTXTBody($data, $isfile = false, $append = false)
    {
        if (!$isfile) {
            if (!$append) {
                $this->_txtbody = $data;
            } else {
                $this->_txtbody .= $data;
            }
        } else {
            $cont = $this->_file2str($data);
            if ($this->_isError($cont)) {
                return $cont;
            }
            if (!$append) {
                $this->_txtbody = $cont;
            } else {
                $this->_txtbody .= $cont;
            }
        }

        return true;
    }
Accessor function to set the body text. Body text is used if
it's not an html mail being sent or else is used to fill the
text/plain part that emails clients who don't support
html should show.

@param string $data   Either a string or
the file name with the contents
@param bool   $isfile If true the first param should be treated
as a file name, else as a string (default)
@param bool   $append If true the text or file is appended to
the existing body, else the old body is
overwritten

@return mixed         True on success or PEAR_Error object
@access public