This code can be applied to "Trigger after update" in a text field to limit the input to rational numbers. It does not accept characters other than "-", [0-9] and ".", otherwise it will set the field to null. Not much can be done about the alignment unless you use the Text field as the value for a Formula field.

"// Initialize variables for negative and leading zero";
"//";
let isNeg := "";
let ldZero := "";
"// Test for zero length string after removing non digit characters and set field to null if true";
"//";
if length(replacex(NoBS, "\D", "g", "")) = 0 then
NoBS := null
else
"// Test for a numeric value of zero and set field to zero if true";
"//";
if number(replacex(NoBS, "\D", "g", "")) = 0 then
NoBS := "0"
else
"// Test for negative, zero or more digits, decimal point, one or more digits. Set field to null if false";
"//";
if not testx(NoBS, "^-?\d*(\.\d+)?$") then
NoBS := null
else
"// Test for negative and set variable if true";
"//";
if substr(NoBS, 0, 1) = "-" then
isNeg := "-"
end;
"// Test for decimal point in lead position. If true set leading zero variable";
"//";
if substr(replacex(NoBS, "^-?0*", "g", ""), 0, 1) = "." then
ldZero := "0"
end;
"// Build final string and assign to field";
"//";
NoBS := isNeg + ldZero + replacex(NoBS, "^-?0*|0+$", "g", "")
end
end
end

This will preserve numeric precision, but if you use the number() function with the value of the text field it will lose its precision. Btw, NoBS is the field's name in this case.