article about tabstop generation

doc/examples/tabstop-generation/README.md

@@ -0,0 +1,50 @@
+# Dynamic tabstop generation
+
+![gif](https://raw.githubusercontent.com/SirVer/ultisnips/master/doc/examples/tabstop-generation/demo.gif)
+
+UltiSnips at the present day is more than snippet engine. It's more like
+constructor, where you can implement some complex features without prior
+feature implementation in the snippet byy itself.
+
+One of that features is dynamic tabstop generation.
+
+Consider case, where you want set of snippets for inserting latex rows of
+various lengths. No-brainer solution is just implement snippet for every
+row length you're possible will want, like this:
+
+```
+snippet tr9 "LaTeX table row of length nine"
+$1 & $2 & $3 & $4 & $5 & $6 & $7 & $8 & $9
+endsnippet
+```
+
+But soon it becomes a burden to maintain that kind of snippets.
+
+Gladly, tabstops can be generated by using anonymous snippet expansion:
+
+```
+global !p
+def create_row_placeholders(snip):
+    # retrieving singlee line from current string and treat it like tabstops
+    # count
+    placeholders_amount = int(snip.buffer[snip.line].strip())
+
+    # erase current line
+    snip.buffer[snip.line] = ''
+
+    # create anonymous snippet with expected content and number of tabstops
+    anon_snippet_body = ' & '.join(['$' + str(i+1)
+                                    for i in range(placeholders_amount)])
+
+    # expand anonymous snippet
+    snip.expand_anon(anon_snippet_body)
+endglobal
+
+post_jump "create_row_placeholders(snip)"
+snippet "tr(\d+)" "latex table row variable" br
+`!p snip.rv = match.group(1)`
+endsnippet
+```
+
+Snippet is declared via regular expression and will expand to any required
+number of fields in row.