[Gmsh] Adaptive meshes in GMSH

[Gmsh User]

Hello everyone,
I have been wondering if it were possible to obtain adaptive meshes with Gmsh.
By adaptive meshes I mean those with variable characteristic length set by the
user. If this is possible, I'd appreciate if some one could point me to
appropriate tutorial/example/manual page. It'd be nice if we can define how
characteristic length varies at different points in .geo file so that we obtain
an adaptive mesh when we mesh the geometry in Gmsh.
I would like to use this feature to make finer meshes along the domain boundary
and also along the material interfaces (for problems related to calculating
electromagnetic Greens function using finite element method).

Thank you in advance for your help.

~Gmsh User