$child_nodes_ar     ar: Array Reference
$attributes_hr      hr: Hash Reference
$callback_cr        cr: Code (or Callback) reference
$next_node_it       it: Iterator
$report_fhi         fhi: File Handle for Input   *1
$summary_fho        fho: File Handle for Output  *1
$time_re            re: Regexp

##</code><code>##

$yesterday_dt       dt: Date::Time
$website_ht         ht: HTML::Template
$website_tt         tt: Template Toolkit
$sessions_slct:     slct: IO::Select 
$www_sck            sck: a socket of kinds (most likely IO::Socket)

##</code><code>##

$input_buf          buf: a buffer
$valid_b            b: used as a boolean
$entities_cnt       cnt: count, or ammount
$log_f              f: a format for sprintf() or printf()
$article_id         id: a unique identifier
$element_idx        idx: an index
$session_ser        ser: a serialized object
$long_name_out      out: output value for the current subroutine

##</code><code>##

$report_html        html: content in html format
$report_json        json: content in json format
$report_txt         txt: content in plain text format
$report_yaml        yaml: content in yaml format 
$report_xml         xml: content in xml format

##</code><code>##

@nodes_s            s: stack (so I should only use push, pop, and $node_s[-1] on it)
@nodes_q            q: a queue (so I should only use push, shift, and $node_q[0] on it)
@nodes_out          out: output value for the current subroutine