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I believe that the following (tested) code provides a simple, yet complete answer to my question:

First, for functional surfaces (z=f(x,y)), the following code provides an alternative to the solution invoking the class ParametrizedSurface3D: here we only use parametric_plot3d:

M=5
funcsurfplot=[0 for i in range(M)]
x, y = var ('x, y', domain='real') 
n=var('n', domain='integer')
funcsurfplot=[parametric_plot3d((x, y, exp(-(x^2+y^2)/(n+1))), \                                                                                         (x, -2-n, 2+n), (y, -2-n, 2+n), \                                                                                                                                     color=rainbow(M)[n], opacity=0.3,  mesh=True) for n in range(M)]
P=sum(funcsurfplot[i] for i in range(M))
P.show(viewer='jmol')

Note that in this case we have full control over the domains of each of the functions in the family of surfaces, and that these domains can also depend on the integer parameter of the family. The line "funcsurfplot=[0 for i in range(M)]" might be considered redundant, but I prefer it for creation of array-like list in Python with custom size, because, unlike the use of 'append', this approach allows the easy construction of multidimensional arrays (two dimensional arrays would be needed for visualizing the families of coordinate surfaces in the example I gave in the formulation of the question) -- see, e.g.,

http://www.i-programmer.info/programm...

Now all the other cases of the question can be resolved in the same simple uniform way, as follows:

Second, meshes of 3D curves (curvilinear coordinates in 3D and on surfaces):

M=5
curve3dplot=[0 for i in range(M)] # creation of array of size M+1 via initialization
t=var ('t', domain='real')
n=var('n', domain='integer')
curve3dplot=[parametric_plot3d((exp(-(n+t)^2), cos(n*t*pi), 1/(1+n*t^2)),  (t, -1, 1), \                                 color=rainbow(M)[n], thickness=4) for n in range(M)]
P=sum(curve3dplot[i] for i in range(M))
P.show(viewer='jmol')

Third, families of parametric surfaces (the surfaces chosen here are Klein bottles of the default type in SAGE - see

http://doc.sagemath.org/html/en/refer...

and, in order to introduce dependence on n also in the parametric domains, I have slightly 'unzipped' them):

M=5 
parasurf3dplot=[0 for i in range(M)] 
u, v = var ('u, v', domain='real') 
n=var('n', domain='integer') 
def fx(u,v,n): return ((n+1)/M+cos(u/2)*cos(v)-sin(u/2)*sin(2*v))*cos(u) 
def fy(u,v,n): return ((n+1)/M+cos(u/2)*cos(v)-sin(u/2)*sin(2*v))*sin(u) 
def fz(u,v,n): return sin(u/2)*cos(v)+cos(u/2)*sin(2*v) 
def rangeu(n): return (u, -pi+(n/M^3)*pi,pi-(n/M^3)*pi) 
def rangev(n): return (v, -pi+(n/M^3)*pi,pi-(n/M^3)*pi) 
parasurf3dplot=[parametric_plot3d((fx(u,v,n), fy(u,v,n), fz(u,v,n)), rangeu(n), rangev(n), \        color=rainbow(M)[n], opacity=0 ...

To begin with a warning: I am a very experienced mathematician but a complete – 'greenhorn' – beginner in SAGE. I would like to be able to plot in the same 3D plot FAMILIES OF PARAMETRIC CURVES IN 3D (x(i)=x(t,i),y=y(t,i),z=z(t,i)) plotted via e.g. parametric_plot3D DEPENDING ON A NON-NEGATIVE INTEGER PARAMETER i in range(I+1) where the coordinate functions x,y,z are defined as functions of t by me and are not necessarily predefined SAGE functions, and where I can vary the non-negative integer I without varying the code. I would like to do the same for FAMILIES OF FUNCTIONAL SURFACES (z=f(x,y,i), DEPENDING ON A NON-NEGATIVE INTEGER PARAMETER i) using e.g. ParametricSurface, as well as TO DO THE SAME for FAMILIES OF PARAMETRIC SURFACES ( (fx(u,v,i),fy(u,v,i),fz(u,v,i)) ) via using e.g. parametric_plot3D DEPENDING ON A NON-NEGATIVE INTEGER PARAMETER i in range(I+1. I would also like to be able to do the same for FAMILIES OF IMPLICITLY DEFINED SURFACES IN 3D DEPENDING ON A NON-NEGATIVE INTEGER PARAMETER i, using e.g. implicit_plot3d ( (f(x,y,z)-C(i)==0, I in range (I+1)), C being a 1-dimensional array (in general algorithmic language) with entries – real numbers in the range of the values of the real-valued f), with the possibility of custom definition of f, I and C. Examining the SAGE tutorials and reference manuals, I have so far been able to find a model solution of this problem only for planar curves in 2D using plot() and only for SAGE-predefined curves (namely, polynomial curves): http://sage.maa.org/home/pub/140/

sage: lotsa_plots = sum([plot(x^n,(x,0,1),color=rainbow(5)[n]) for n in range(5)]) Already in this simple 2D case, if the SAGE-predefined function x^n in the above example be replaced by a custom-defined function f(x,n) , it is not clear to me (a greenhorn!) how to extend the above instance to plotting together the 2D graphs of f(x,n), color=rainbow(N)[n]) for n in range(N), where one should be able to vary N withouth modifying the SAGE code. I think that providing examples solving the above tasks in the SAGE tutorials/manuals (or developing SAGE in this direction if the tasks are currently SAGE-unsolvable!) is of key importance FOR A GREAT MANY OF THE USERS (OR WANNABE USERS) OF SAGE WHO ARE EXPERIENCED THEORETICIANS BUT ARE NOT EXPERIENCED PROGRAMMERS. To facilitate the eventual answering of these questions, I herewith propose a simple but comprehensive example. IF YOU PROVIDE COMPLETE ANSWERS CONCERNING THIS EXAMPLE, YOU WILL HAVE ANSWERED ALL OF THE ABOVE QUESTIONS TOGETHER. Moreover, your answer would certainly merit to be included among the examples in the next version(s) of the SAGE tutorial[(s) and/or reference manual(s).
Consider the 3D scalar field (argument is a 3D vector ...
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