T cl ▁is ▁a ▁subset ▁of ▁T cl ▁that ▁has ▁restricted ▁features ▁so ▁that ▁T cl ▁scripts ▁cannot ▁harm ▁their ▁hosting ▁machine ▁or ▁application . ▁File ▁system ▁access ▁is ▁limited ▁and ▁arbitrary ▁system ▁commands ▁are ▁prevent ed ▁from ▁execution . ▁It ▁uses ▁a ▁dual ▁interpreter ▁model ▁with ▁the ▁un tr usted ▁interpreter ▁running ▁code ▁in ▁an ▁un tr usted ▁script . ▁It ▁was ▁designed ▁by ▁Nathan iel ▁Bor en stein ▁and ▁Marshall ▁Rose ▁to ▁include ▁active ▁messages ▁in ▁e - mail . ▁Sa fe - T cl ▁can ▁be ▁included ▁in ▁e - mail ▁when ▁the ▁application / safe - t cl ▁and ▁multip art / enabled - mail ▁are ▁supported . ▁The ▁functionality ▁of ▁Sa fe - T cl ▁has ▁since ▁been ▁incorpor ated ▁as ▁part ▁of ▁the ▁standard ▁T cl / T k ▁releases . ▁ ▁Syntax ▁and ▁fundamental ▁semantics ▁ ▁The ▁syntax ▁and ▁semantics ▁of ▁T cl ▁are ▁covered ▁by ▁twelve ▁rules ▁known ▁as ▁the ▁D ode kal og ue . ▁ ▁A ▁T cl ▁script ▁consists ▁of ▁a ▁series ▁of ▁command ▁inv oc ations . ▁A ▁command ▁inv ocation ▁is ▁a ▁list ▁of ▁words ▁separated ▁by ▁whitespace ▁and ▁terminated ▁by ▁a ▁newline ▁or ▁sem icol on . ▁▁ ▁word 0 ▁word 1 ▁word 2 ▁... ▁word N ▁ ▁The ▁first ▁word ▁is ▁the ▁name ▁of ▁a ▁command , ▁which ▁may ▁be ▁built ▁into ▁the ▁language ▁or ▁found ▁in ▁an ▁available ▁library ▁( or ▁defined ▁in ▁the ▁script ▁itself ); ▁the ▁subsequent ▁words ▁serve ▁as ▁arguments ▁to ▁the ▁command :