string chunk

jbr - 2013-06-16

 # Chunk a string into bite sized pieces.
 #
 proc ::tcl::string::chunk { data { size 70 } } {
    set len [expr { $size -1 }]

    for { set i 0 } { $i < [string length $data] } { incr i $size } {
        lappend reply [string range $data $i $i+$len]
    }

    set reply
 }

 namespace ensemble configure string -map [dict merge [namespace ensemble configure string -map] {chunk ::tcl::string::chunk}]

Cribbed from dict lappend2