arw (Dec 2015): here is an example of a fontmap when exporting the canvas content to a postscript

======
package require Tk

canvas .c
pack .c -fill both -expand TRUE

set txt "Lorem ipsum dolor sit amet..."
.c create text 50 40 -text $txt -anchor w -font "*-Helvetica-Medium-R-Normal-*-12-*" 
.c create text 50 80 -text $txt -anchor w -font "*-Times-Bold-R-Normal-*-14-*" 
.c create text 50 120 -text $txt -anchor w -font "*-Courier-Normal-R-Normal-*-16-*"

set fm(*-Helvetica-Medium-R-Normal-*-12-*) [list Helvetica 12]
set fm(*-Times-Bold-R-Normal-*-14-*) [list Times 12]
set fm(*-Courier-Normal-R-Normal-*-16-*) [list Courier 12]

.c postscript -file test.ps -fontmap fm
======


However, I don't know how to get the https://www.tcl.tk/man/tcl8.6/TkCmd/font.htm#M5%|% X-font names%|% for an arbitrary font created with `font create`, for example,

======
package require Tk
set tt [toplevel .1]

pack [canvas .1.c] -fill both -expand TRUE

set dv [font create -family {DejaVu Sans}]

.1.c create text 100 50 -text "Hello World" -font $dv
======


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