How does data bind paranthesis work in Knockout.js

I have this input and I want to change its status, so it can be readonly or editable.

<input type="text" data-bind="attr: {readonly: isViewMode || isNotEditableInvoice}, value: model.DateFormatted" />

The problem is when I don't use paranthesis for the variables.

First case: isViewMode = true, isNotEditableInvoice = false => readonly is evaluated to true

Second case: isViewMode = false, isNotEditableInvoice = true => readonly is evaluated to false

Also I have this button, and I want to show it only when the user is in edit mode.

<input type="button" value="Save" data-bind="visible: !isReadOnly || isEditableInvoice,click: onUpdate" />

I have a similar problem with using paranthesis, and I want to know what is happening there.

Third case: isReadOnly = false, isEditableInvoice = false => visible is set to false

Fourth case:
When I use paranthesis for isReadOnly it's working fine, the result is the same as above, but somehow it is evaluated to true. Why isEditableInvoice is excluded from evaluation without paranthesis?
<input type="button" value="Save" class="btn btn-primary" data-bind="visible: !isReadOnly() || isEditableInvoice,click: onUpdate" />

Why is this happening when I don't use paranthesis and what is the logic behind?

Because the knockout parser/binder is checking that you are binding against an expression ( instead lets say of a single property ) so it will evaluate the expression as-is.

Unless you explicitly call the evaluation a.k.a add the parenthesis at the end, you are just evaluating the expression '!isReadOnly || isEditableInvoice' and the fields are not treated as observables, rather as-is.

isReadOnly is evaluated in js terms as non-undefined, hence true.

For example a different bind, made against a single property would be like the if/visible binds.

You can do

data-bind="if: model.someObservableProp"

but you can not do

data-bind="if: !model.someObservableProp"

without adding the parenthesis like so:

data-bind="if: !model.someObservableProp()"

Because as soon as you add the ! operator, the parsers treats this as a js expression, not as an observable field