We start to put TAGS in simgrid source code for having tutorials to see where is the important parts ans steps to create:

a new MSG functions or a new API.
a new model in surf.
new tags in xml files

How to add a new MSG function?

Search for expression "TUTORIAL: New API".

user@caraja:~/workspace/simgrid/src$ cg "TUTORIAL: New API"
 0 msg/msg_new_api.c             15 /* TUTORIAL: New API*/
 1 simix/smx_smurf.c            582 /* TUTORIAL: New API*/
 2 simix/smx_smurf.c            616 /* TUTORIAL: New API*/
 3 simix/smx_smurf_private.h    102 /* TUTORIAL: New API*/
 4 simix/smx_smurf_private.h    629 /* TUTORIAL: New API*/
 5 simix/smx_private.h           28 /* TUTORIAL: New API*/
 6 simix/smx_private.h          101 /* TUTORIAL: New API*/
 7 simix/smx_private.h          182 /* TUTORIAL: New API*/
 8 simix/smx_global.c           454 /* TUTORIAL: New API*/
 9 simix/smx_new_api.c            8 /* TUTORIAL: New API*/
10 simix/smx_user.c            1684 /* TUTORIAL: New API*/
11 simix/smx_new_api_private.h    8 /* TUTORIAL: New API*/
12 simix/smx_process.c          338 /* TUTORIAL: New API*/

How to add a new model in surf?

Search for expression "TUTORIAL: New model".

user@caraja:~/workspace/simgrid/src$ cg "TUTORIAL: New model"
0 surf/new_model_private.h   2 /* TUTORIAL: New model
1 surf/surf.c              213 /* TUTORIAL: New model*/
2 surf/surf_config.c       380 /* TUTORIAL: New model*/
3 surf/surf_config.c       746 /* TUTORIAL: New model*/
4 surf/new_model.c           8 /* TUTORIAL: New model*/
5 include/surf/surf.h      157 /* TUTORIAL: New model*/
6 include/surf/surf.h      345 /* TUTORIAL: New model*/
7 include/surf/surf.h      661 /* TUTORIAL: New model*/

What is How to add a new tag for xml files?

Search for expression "TUTORIAL: New TAG".

user@caraja:~/workspace/simgrid/src$ cg "TUTORIAL: New TAG"
0 surf/sg_platf.c                    43 /* TUTORIAL: New TAG*/
1 surf/sg_platf.c                    89 /* TUTORIAL: New TAG*/
2 surf/sg_platf.c                   124 /* TUTORIAL: New TAG*/
3 surf/sg_platf.c                   337 /* TUTORIAL: New TAG*/
4 surf/surfxml_parse.c              769 /* TUTORIAL: New TAG*/
5 surf/surf_private.h               205 /* TUTORIAL: New TAG*/
6 surf/surfxml_parseplatf.c          64 /* TUTORIAL: New TAG*/
7 surf/surfxml_parseplatf.c          85 /* TUTORIAL: New TAG*/
8 include/simgrid/platf_interface.h  42 /* TUTORIAL: New TAG*/